Wikipedia:CHECKUSER

CheckUser data may be used to investigate, prevent, or respond to:

The tool may never be used to:

The primary purpose of CheckUser is the prevention of sock-puppetry, but community policy provides for several legitimate uses of alternative accounts where the alternative accounts are not being used to violate site policy (such as by double voting or by giving the impression there is more support for a position in a discussion or content dispute).

Checkusers are permitted, but not required, to inform an editor that their account has been checked. The result of a check may be disclosed to the community (on a community process page like ).

These conventions arise out of practice that has emerged in the years since the checkuser tool was created, and in some cases out of rulings or "statements of best practice" by the Audit Subcommittee (now disbanded) and the Arbitration Committee.

In some situations, while CheckUsers can endeavour to avoid explicitly connecting an account to an IP address, they will find it difficult or impossible not to do so. For instance, when a user edits disruptively using multiple IPs, or a mixture of IPs and accounts, the CheckUser will find it difficult to block the accounts and then the IP addresses without obvious inference being drawn by onlookers from the series of blocks being made in a short period of time. When a user abusively uses several accounts, and it is reasonably plausible they will create more accounts, the underlying IP range must be blocked so that further abusive accounts cannot be made. The IP addresses and user accounts must therefore be blocked together.

Users who engage in problematic conduct to the point that requests for administrative action or blocking are raised and considered valid for CheckUser usage—and where CheckUser then determines the user probably has engaged in such conduct—must expect the protection of the project to be given a higher priority than the protection of those who knowingly breach its policies.

advises that, even if the user is committing abuse, personal information should if possible not be revealed. Checkusers are advised as follows:

"Fishing" is to check an account where there is no credible evidence to suspect sockpuppetry. Checks are inappropriate unless there is evidence suggesting abusive sock-puppetry. For example, it is not fishing to check an account where the alleged sockmaster is unknown, but there is reasonable suspicion of sockpuppetry, and a suspected sock-puppet's operator is sometimes unknown until a CheckUser investigation is concluded. Checks with a negative result do not mean the check was initially invalid.

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Wikipedia