Use it for questions related to site security, in particular those focused on protecting a Drupal site from unauthorized access.
Site security is about a number of topics related secure administration of a Drupal website. If the security question is not specific to Drupal, it may be better to ask the question on one of the following StackExchange sites:
- If it is about security in general: Information security
- If it is about web site security (but not specific to a Drupal web site): Pro Webmasters
- if it is about managing system security in a professional capacity: ServerFault
Topics that can be asked about using the security tag includes, but are not limited to: limiting access to the site or parts of the site, dealing with (including blocking) malicious users and robots, protecting of the site's public and private files, protecting sensitive content such as password, and using encryption and other methods to improve site security.
Please note that site administrators should also sign up for the security mailing list. People interested in further discussing security should join the Drupal.org group Best Practices in Security Group.