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Some of Wikipedia's pages on anonymity:
- Wikipedia talk:Talk page/Anonymous talk pages proposal
- Wikipedia:Changing attribution for an edit (not functional since early 2005; see Bugzilla #3539 for an automated idea)
This is "an official policy approved by the Wikimedia Foundation Board of Trustees. This policy may not be circumvented, eroded, or ignored on local Wikimedia projects."
Summary: If you only read the Wikimedia project websites, no more information is collected than is typically collected in server logs by web sites in general. If you contribute to the Wikimedia projects, you are publishing every word you post publicly. If you write something, assume that it will be retained forever. This includes articles, user pages and talk pages. Some limited exceptions are described in the main policy.
Checkuser Policy 
See also: Editor's index: privacy
See for instance these guidelines:
- Wikipedia:Username policy
- Wikipedia:Changing username
- Wikipedia:Right to vanish and m:Right to vanish
- Wikipedia:Wikipedia is anonymous
- Wikipedia:Welcome anonymous editing
- Wikipedia:IPs are human too
- Wikipedia:The overuse of anonymity at Wikipedia and a proposal
- Wikipedia:How to not get outed on Wikipedia
Rejected guidelines 
- Wikipedia:Editors should be logged in users
- Wikipedia:Disabling edits by unregistered users and stricter registration requirement
At some point in 2003, there were role accounts on en:wp and on fr:wp. They are currently (as of late 2005) considered harmful.
Technical implementations 
- Bugzilla #550 – blocking IPs without affecting formerly-created accounts (long discussion; should be combined with a throttle on # of account creations per IP per [day])