Security Basics: Re: debian system users delete or change access

[byteme () microsoft com]

You can delete them... but things may stop working. 

If it's named after a function like.. irc, or uucp, you can probably remove it if you don't use it. 

You should leave the ones below alone. They system uses them for various things even though the may sound useless. 

daemon:x:1:1:daemon:/usr/sbin:/bin/sh
bin:x:2:2:bin:/bin:/bin/sh
sync:x:4:65534:sync:/bin:/bin/sync
man:x:6:12:man:/var/cache/man:/bin/sh
proxy:x:13:13:proxy:/bin:/bin/sh
backup:x:34:34:backup:/var/backups:/bin/sh
operator:x:37:37:Operator:/var:/bin/sh
nobody:x:65534:65534:nobody:/nonexistent:/bin/sh

If you're going to delete, backup your /etc/passwd and /etc/shadow before hand. If something stops working after you 
delete it, put it back.