When I was on holidays about a month ago... I logged into my ebay account from a different IP address (my sister) and I tried to do some maintenance on my listings so I wouldn't have to do it when I got home... the system would not allow me to. Which at the time I was annoyed but in hindsight I think it is a good thing....

Definately have an investigation done by ebay.... as previously advised they can track the history of your account etc... and once verified that it was not you but from a rogue they hopefully will look after you.

Also CHANGE ALL PASSWORDS NOW!!!!