Have I been hacked?

["Ian Goodall" <ijg@iangoodall.co.uk>]

I am running a debian woody server and when I checked the last users
yesterday I a large number of logins in the list. On running the command
today I get the following:

dev1:/home/ian# last
ian      pts/0        172.16.3.195     Wed May  7 14:49   still logged in
team1    pts/0        blue99.ex.ac.uk  Wed May  7 13:21 - 13:57  (00:35)

I have run chkrootkit but nothing was found.

I have never had this before. Am I being paranoid or is someone trying to
cover up their tracks?

Thanks

ijg0