- You can use rkhunter (
http://freshmeat.net/projects/rkhunter/) and chkrootkit (
http://www.chkrootkit.org/) to scan your machine against root-kits.
- You can check for any `new' and interesting ports that are listening.
- You can check for any `new' and interesting programs that are running.
- You can search for any strange commands in your shell history (if not deleted).
- You can look at the login logs or syslog messages.
- You can look at the /etc/passwd and /etc/group files for any newly created user accounts.
- You can try to reinstall these tools,.. and so on.
PS: Hackers don't attack you, crackers do. Please use the correct terms (RFC 1392)