Debian

Many people misunderstand the usefulness of identd, and so disable it or block all off site requests for it. identd is not there to help out remote sites. There is no way of knowing if the data you get from the remote identd is correct or not. There is no authentication in identd requests.

Why would you want to run it then? Because it helps you out, and is another data-point in tracking. If your identd is not compromised, then you know it's telling remote sites the user-name or UID of people using TCP services. If the admin at a remote site comes back to you and tells you user so-and-so was trying to hack into their site, you can easily take action against that user. If you are not running identd, you will have to look at lots and lots of logs, figure out who was on at the time, and in general take a lot more time to track down the user.

The identd that ships with most distributions is more configurable than many people think. You can disable it for specific users (they can make a .noident file), you can log all identd requests (We recommend it), you can even have identd return a UID instead of a user name or even NO-USER.