I have a large dedicated server running Debian and I want to share it with about 6 friends of mine. I know I can simply just use adduser to create user accounts for them, but I want to know if they can, even as a regular user without root permissions, do anything malicious.

I know by default they have read permissions for other users in the /home, and can solve that with chmod, but I just want to make sure that there's nothing else they can do.

And also, is there any kind of script or program that makes it easier to create and manage shell users on a server?