DOKK Library
      An Open Letter from the Mastodon Community
                         Administrators, Scholars and Users
                                     January 20, 2020

    We are writing to raise grave concerns regarding the ethics and methodology of “Mastodon
Content Warnings: Inappropriate Contents in a Microblogging Platform”, by Matteo Zig-
nani et al. of the University of Milan. The issues with this paper are sufficiently severe
that the paper’s dataset has been removed from Harvard’s Dataverse repository. This open
letter will explain the background of this removal and urge further action on the part of
the paper’s authors, the University of Milan, and the Association for the Advancement of
Artificial Intelligence (AAAI), who have published the paper in their conference proceedings.
As we detail below, the data analysed in this paper was not collected ethically, failing to take
even simple steps to anonymize the data released with the paper, and fundamental errors of
methodology make its results irrelevant.
    Mastodon is a decentralized, community-operated microblogging platform created in
early 2016 by Eugen Rochko and is based on open protocols that allow people to communi-
cate across different servers. Anyone who wishes to create a Mastodon server, or instance,
can do so by downloading and installing the Mastodon software. Users who register accounts
at an instance can then share social-media posts with other users on that instance as well
as with other instances. The interconnection of different servers is known as federation.

1    Violation of Terms of Service
The authors state that they are aware that the Terms of Service and privacy policies vary from
one Mastodon instance to the next: “Even though the distributed nature of Mastodon allows
each instance adopts a specific terms of use and service, many instance [sic] are used to adopt
the standard terms of service and privacy policy provided by the Mastodon developers.” It
is evident, however, that they did not respect the Terms of Service and privacy policies
of all the instances scraped into their dataset. For example, the instance
documentation plainly states as follows:
     Researchers who wish to study Scholar Social or our users by collecting data
     using the API or through any other means that does not involve an “opt-in”
     from individual users are required to submit their protocol, analysis plan and
     all relevant ethics approval documentation from their institutional review board
     or departmental internal review documentation by email to:

      at protonmail dot-com. You may also be required to submit code you plan
      to execute so that it can be tested to ensure it does not degrade the quality of
      service to other users.
      This does not apply to, e.g. surveys circulated on Scholar Social that individ-
      ual users can consent to participating in. This does apply to database scraping
      software, or any means of recording user activity where our users might be sur-
      prised that they were included afterward, because they were not given a chance
      to consent.
      Many of our users came to Scholar Social in order to avoid being included in
      unethical social media research, and so we place a higher value on conducting
      research on human subjects with informed consent than most other social media,
      in order to maintain high ethical standards.
      At the admin’s discretion, you may be asked to submit your research protocol,
      and the institution that is providing ethical review, even in the case that it is an
      opt-in survey. Failure to disclose your research plan may result in closure of your
      account, or having your network banned from our service.

   Note that 10487 posts from the domain were captured in the dataset
formerly available under doi:10.7910/DVN/R1HKVS, as measured by

    cat timeline_*.jsonl | jq .uri | grep | wc -l

2     Failure to de-identify data
The authors state that “Since the Mastodon user may be unaware of their data being public
and reusable for research purposes we disposed of the information about the users and we
fully anonymized them by hashing the Mastodon user identifier.” Unfortunately, this is not
the case. The authors appear to have neglected the uri field in the data for each toot. This
field contains both the domain name of the instance as well as the user’s name and number.
This information identifies the post and the Mastodon user who made it, in all of the data
that Zignani et al. scraped, aggregated, and made available to the world. The URI as-is can
be used by anyone in the world to directly view the original post through their browser (if
the post’s visibility is “Unlisted” or “Public”, as described below). The URI also contains a
timestamp on when the post has been published (in milliseconds after 1970, UNIX time) and
thus provides the means to identify when certain users have been online over a long term.
Consequently, the authors’ dataset consists of posts that have been scraped and reproduced
not just without users’ consent, but also without anonymization.
    This contradicts both the authors’ claim as well as requirements outlined by the GDPR.
    We note that the uri field is visible in the authors’ Figure 2, “An example of [a] toot in
JSON format”. It is difficult to imagine how this part of the data could have been neglected.
    Moreover, the authors make no mention of de-anonymization, the practice of discovering
the authorship of supposedly anonymous material. Simply put, content itself can reveal its

creator’s identity even after metadata has been removed. Distributing a dataset without
regard for this possibility is highly irresponsible.

3    Fundamental mistakes of data analysis
The topic nominally being addressed by Zignani et al. is the matter of “inappropriate”
content on social media. Posts on most Mastodon instances are known as “toots”, a jocular
reference to the sound that a large elephant-like mammal would make. The Mastodon
software allows the user to hide the text of their toot behind a subject line, or “Content
Warning”. When such a toot is viewed, only the subject line is visible, until a “show more”
button is clicked, whereupon the text is revealed. Zignani et al. clearly state that they use
Mastodon’s Content Warning feature to determine which toots are “inappropriate”:

     By clicking on the “CW” button, a user can enter a short summary of what the
     “body” of her post contains, namely a spoiler-text, and the full content of her
     toot. Automatically, the system marks this toot as “sensitive” and only shows
     the spoiler-text in all the timelines. We exploit this latter feature to build our
     released dataset. This way the toots are labelled by the users, and we assume
     that they are aware of the policy of the instance and aware of what is appropriate
     or not for their community.

But this reveals a fundamental misunderstanding of the Mastodon community and how the
software is used in practice. Even a brief time spent actually using the software makes
clear that Content Warnings have many uses and do not always indicate posts that are
“inappropriate” by any standard. A user can click the “CW” button to label a toot as
containing discussion of politics, illness, injury, or bigotry (sexism, racism, homophobia,
transphobia, and so forth). All of these topics are “appropriate”, but a user may at their
own discretion decide to provide advance warning for the benefit of those readers who wish to
mentally prepare themselves for reading about emotionally damaging subject matter. Such
CWs are acts of courtesy, not signals of “inappropriate” content. Users often apply CWs to
toots about food and cooking, topics that are safe for children to read but may cause distress
among readers with eating disorders. CWs can also hide spoilers about movies, books and
television shows, and they can be part of the presentation of a joke: the “Content Warning”
text contains the setup, and clicking to open the toot then reveals the punchline. By no
stretch of the imagination is hiding the punchline of a joke an example of content that strays
outside of community norms or that “may hurt people’s feelings”.
    The authors’ own figures cast intense doubt upon their identification of Content Warn-
ings with “inappropriate” material or “bad content”. We note the prominent placement of
“cauliflower” and “cheesesteak” in the word cloud of “inappropriate” material on mastodon
.social, and the comparable prominence of “patient”, “medication” and “healthcare” in
the word cloud. It is not often that we wonder if the authors of an academic
paper have looked at their own plots, but this is one of those times.

    We can only describe the authors’ discussion of Content Warnings as a total failure of
comprehension, and we question the value of any research based on such a faulty grasp of
how the Mastodon community operates. The authors claim, “The usage of this dataset
empowers researchers to develop new applications as well as to evaluate different machine
learning algorithms and methods on different tasks”, but we see little chance of empowerment
when the foundations are so flawed. As that old computer-science motto has it, garbage in,
garbage out.

4     Mistaken classification of post privacy
The authors state that “Each toot has a privacy option, and users can choose whether the
toot post is public or private,” going on to describe “public messages”, “private messages”,
and “local timeline” messages. The authors have unfortunately conflated two things: the
way the Mastodon web interface aggregates posts, and the post privacy selections available to
Mastodon users through that same interface. A cursory inspection of the Mastodon interface
or the onboarding guide made available to new users makes clear the privacy settings, of
which there are four :

    • Direct message: These posts are visible only to the sender, the mentioned users, and
      the administrators of the users’ respective instances.

    • Followers only: These posts are only available to users’ followers, and cannot be
      boosted (i.e., “retweeted”, except by the originating user). Notably, these posts cannot
      be accessed by navigating a browser to the post’s URL. This amounts to an explicit
      refusal of consent to scrape or copy the post.

    • Unlisted : These posts may be boosted by any user that views them, and may be
      viewed by anyone with access to the post URL. However, they are not included in
      the aggregated timelines provided by the Mastodon user interface. This post privacy
      setting is specifically intended to allow circulation of a post without consenting to
      release of a post outside of Mastodon itself, as review of public Mastodon development
      discussions on Github would have revealed.

    • Public: These posts are similar to unlisted posts, but also allow distribution to other
      instances with which the user’s home instance federates. Importantly, users can opt
      out of allowing search engines to index their public posts.

The Mastodon user interface provides a local timeline, which is a live, reverse-chronological
list of the public posts on the user’s home instance. In addition, it provides a federated
timeline, a live, reverse-chronological list of the public posts from a wider realm. Typically,
the federated timeline of an instance contains all the public posts of all the users followed by
any user on that instance. This allows rapid dissemination of posts among instances. Posts
on local and federated timelines may or may not be open to indexing by search engines.

    From a research standpoint, the authors’ ignorance of the four visibility types and con-
flation of those types with post aggregation in the interface has not only led to a breach of
ethics, but also a surprising lack of rigor. As indicated above, simply using the Mastodon
interface would have dispelled half of the authors’ ignorance, and a rigorous methodology
consistent with peer-reviewed research work would have included research into the reasons
for these visibility types.
    Many Mastodon users, including the authors of this letter, are scientists with extensive
experience writing and reviewing scholarly articles. Given these serious issues, we would not
have accepted a paper in this condition for publication.

5    GDPR compliance issues
The authors state that their dataset is stored in Europe and thus protected by the GDPR,
with which they erroneously claim they have complied. However, Harvard Dataverse had
made this dataset available through their own infrastructure. It is unclear if this complies
with GDPR requirements. That notwithstanding, the ethical breaches and lack of consent
as detailed above similarly preclude release of the data by Harvard Dataverse. We express
our gratitude for the prompt deaccessioning of the dataset from the Harvard Dataverse

6    Relicensing and redistribution of copyrighted mate-
By posting to the Harvard Dataverse, the authors have released the scraped dataset under
the Creative Commons CC0 license, a choice of license that is tantamount to putting material
in the public domain. This blatant relicensing constitutes, at the very least, a serious misuse
of CC0 and, in our view, a breach of the basic ethical principles underlying the notion of
copyright. Referring again to the Terms of Service:

     User-submitted content, including profile information, avatars, uploaded media,
     posted content, replies and any other information submitted to Scholar Social
     remain the property of the user who submits it (provided they owned it to begin
     with). Scholar Social members and staff do not monetise or sell material posted
     here. Users retain complete creative and legal control of their own submitted
     material. [emphasis added]

Many users came to Mastodon in order to preserve their control over the content they create,
rather than signing it over to one gigantic corporation or another. Attempting a wholesale
relicensing of Mastodon user content is a grievous appropriation. Quoting the Creative
Commons organization themselves, “You should only apply CC0 to your own work, unless
you have the necessary rights to apply CC0 to another person’s work.”

7     Neglect of risk presented to users
A text search of the paper for any of the terms “lgbt”, “minor”, or “margin” finds no
results. This is concerning, especially in a paper that purports to be written with the
goal of addressing “inappropriate” content, which is necessarily a culture-bound concept. A
significant number of Mastodon users are members of ethnic, gender, sexual, and/or many
other minority groups, and as members of marginalized groups, they face a myriad of risks
and harms, including harassment, persecution, and physical harm. (This also applies to
users who are minors.) In other words, a great many of these users are significantly more
vulnerable than users who are members of majority groups. The authors could have learned
of this from any number of public blog posts written by such users, as well as through a
simple aggregate count over the data they themselves scraped without consent.
    As such, ethical concerns regarding this paper and dataset are heightened. The authors’
invasion of such users’ privacy is itself a significant harm, but the unexamined hazards
created by their publication of the dataset are severe. This neglect is egregious. Even the
most cursory research into risks faced by users of color and LGBTQIA+ users around the
world reveals these risks to be quite substantial. These users are the people whose very
existence has been deemed “inappropriate” throughout many social spheres in history, and
this prejudice continues up to the present moment. The published paper as well as the
authors’ methodology should have included due consideration and discussion of these issues.
    Beyond the matters this letter has already detailed, we have also identified other passages
where the paper betrays a lack of familiarity, or even casual acquaintance, with Mastodon
and the existing writings about it. For example, the authors’ description of the
instance reveals ignorance of, or indifference to, a significant chapter in Mastodon history that
has already been documented by technology journalists. These shortcomings contribute to
the paper’s general atmosphere of carelessness, though in our estimation they are less severe
than its ethical lapses and its fundamental misapprehension of data.

8     Lack of Acknowledgment of Funding Sources
The authors fail to disclose their sources of funding. Not only is this unusual for an aca-
demic paper, to say the least, it prevents the reader from investigating whether the work
was done in compliance with the funding agency’s standards for responsible research. The
AAAI claims that submissions to these conference proceedings were “carefully reviewed by
66 senior program committee members, 117 program committee members, and 328 addi-
tional reviewers.” We find it puzzling that this process accepted a paper on anthropological
research which omits an acknowledgment of its funding sources.

9     Remedies
We ask that the authors take the following actions:

   • Apologize publicly in AAAI Proceedings for this violation of vulnerable users’ consent

   • Retract their paper from publication

   • Delete all copies of the dataset they control

   • Disclose their funding sources
We ask that the AAAI take the following actions:
   • Print this letter in its Proceedings

   • Issue a retraction of the “Mastodon Content Warnings” paper until the ethical failures
     have been addressed

   • Should the paper be republished in any form, ensure personally identifiable information
     (such as verbatim posts, usernames, profile pictures, etc.) within screenshots in the
     paper or footnotes is redacted

   • Investigate the review process for its conference proceedings, with particular atten-
     tion to the question of whether the committee members and other reviewers have the
     relevant ethics experience to review social-media dataset papers
We ask that the University of Milan take the following actions:
   • Investigate the basis on which this research was initiated, and whether any junior
     researchers involved were adequately supervised

   • Issue a statement of retraction through the University public-relations system and any
     other means by which the original paper may have been advertised

   • Delete all copies of the dataset they control
We ask that Harvard University take the following actions:
   • Fully commit to the deaccessioning of the “Mastodon Content Warnings” dataset by
     removing it and all backups of it from Dataverse and any other Harvard-owned infras-

10     Signatories of this letter
We are writing as users of Mastodon and other intercompatible software platforms that
participate in the federated social network (the fediverse) of which it is the most visible
component. The opinions we express herein are not official position statements of our em-
ployers or funding agencies.
  1. Noëlle Anthony, owner of academic research firm Anthony Expert Services LLC; ad-
     ministrator of (

 2. Marie Axelsson (

 3. Daniel Bohrer, citizen of (@daniel

 4. Benjamin G Carlisle PhD, Postdoctoral researcher, QUEST (Berlin Institute of Health);
    administrator of (

 5. Maëlan Chapovaloff, administrator of (

 6. Lorenz Diener, administrator of (

 7. Alejandro Gaita-Ariño, Senior Researcher at the Institute of Molecular Science, Uni-
    versitat de València (

 8. Millia Gallé-Tessonneau, administrator of (

 9. Michael Gerdemann, owner and administrator of (

10. Stéphane Guillou, Technology Trainer, The University of Queensland (Library)

11. Gwenfar, Puffin & Joe, administrators of (@GwenfarsGarden,
    @puffinus puffinus,

12. Vieno Hakkerinen, citizen of (@txt

13. Peter Hessler, owner and administrator of (

14. Host, administrator of (

15. Xan Indigo, Postdoctoral Researcher, Université Paris-Sud

16. Martin Kopischke, Head of Production at ifs international film school cologne

17. Tobias Kunze, owner and administrator of (

18. l4p1n, user of (

19. lawremipsum, administrator of and attorney

20. Leonie, administrator of (

21. Sam Lloyd, Cert HE (Open), administrator of

22. Bryce Alexander Lynch, Founder and Administrator, Virtual Adept Networks; Security
    Researcher, Special Circumstances, LLC (

23. maple mavica syrup, BSc in Information Systems, owner and administrator of (

24. Matthew Meier, administrator of and (

25. Erin Moon, Research Assistant, Electrical and Computer Engineering Department,
    University of Wisconsin–Madison; server administrator of

26. Leah Oswald, owner and administrator of (

27. Paul, administrator of and software engineer at Natural History Mu-
    seum, London (

28. Kim Reece (

29. Ros, user of and (

30. Sascha, administrator of (

31. Isabelle Santos, postdoctoral researcher, UniGe (

32. self, administrator of (

33. Katt Sextant, member (

34. Ana Silvia C. Silva, PhD in applied data science (

35. Kaito/Katie Sinclaire, owner of single-user instance (

36. Blake C. Stacey, Research Assistant Professor, Department of Physics, University of
    Massachusetts Boston (

37. Sylvhem, administrator of (

38. The Gibson, admin of and Chief Officer of BlackFireSec

39. Rylie James Thomas, administrator of and

40. Rey S. Tucker, administrator of (

41. Wim Vanderbauwhede, professor in Computing Science, University of Glasgow, UK

 42. Walter Vannini, GDPR consultant and teacher of high-school mathematics

 43. David Wolfpaw, administrator of (

 44. Liaizon Wakest, administrator of and

A      Relevant Articles from the 2019 Codice etico e per
       l’integrità nella ricerca
All quotations are from the official English version. From Article 16, “Feasibility, and social
and environmental impact”:
      Researchers assess the project feasibility, the ethical and legal aspects and, if
      necessary, the social requests and needs it satisfies. Should the project likely
      produce a significant impact on the objects of the research or, in general, on
      society, the environment or the biosphere, researchers shall responsibly examine
      the potential impact, providing details of these assessments in the appropriate
    Article 26, “Informed Consent”:
      Without prejudice to the principle of due respect for human dignity and auton-
      omy, should the research entail the involvement of recruited participants, the
      research leader ensures that applicable norms on informed consent are respected,
      with special regard to incompetent subjects or, in any event, to individuals unable
      to give consent.
    Article 27, “Storage and processing of personal data”:
        1. Storage and processing of personal data shall take place pursuant to applica-
           ble norms and University regulations. Participants in the research shall be
           provided with the names and contact details of the controller and processor
           of personal data.
        2. Processing and storage of personal data of participants recruited for the
           study shall preferably be effected in codified or anonymous form. Should this
           not be possible due to the object of the research or its purpose, researchers
           shall scrupulously observe the provisions in force, in order to ensure due
           respect for the privacy of the persons involved.
    Article 31, “Confidentiality”:
        1. The dissemination of research findings shall take place respecting the privacy
           of all persons involved.

2. If, due to scientific constraints, it is impossible to respect anonymity, per-
   sonal data of research participants may be divulged only in conformity with
   their previous informed consent.

              This open letter is released under the Creative Commons CC0 license.


An Open Letter from the Mastodon Community


License CC0-1.0