Do you happen to be running an AMD SMP processor? Did you just recently upgrade your kernel or glibc? Seems to be a pattern with this error and AMD processors.
Luckily, you are probably not hacked... the error is not coming from a rootkit or anything. I would be a little concerned about the login you don't recognize, but it is probably unrelated.
Originally posted by Sasuke I'd be more then a little concerned, somebody that he doesn't know has logged into his server.
I am thinking that he will eventually realize that he logged in from his buddy's house or it was his service provider or a remote tech. Generally, hackers who gain root access won't be dumb enough to leave lastlog entrees.