Um, I hope this isn´t a "how can I crack my own account"-thing...
Forget the account and get a new one, it´s a good opportunity to get rid of people which you don´t want on your buddy-list any more too...
The important question is: How was it possible to successfully use a keylogger on you? Points to a big lack of security of your system, mate...
You should check regularly the processes running in the background, opened ports, system startup settings (I recommend at least once a day) and do a full system scan for malware at least once a week.
But now that you found the keylogger I hope you took the opportunity to get the logfile destination IP for a little payback....
