Account locked for suspicious activity?

when i came home after work, i went to log into wow, and it said that my account was locked due to suspicious activity. later, i got an email saying i needed to change my password. i changed my password, and checked ingame to see if anything was missing from my account. there was nothing i could see missing. i asked guildies if i had been online previously. they said no. can i get any feedback on what was the suspicious activity so i know whether was something i did or whether my account was actually compromised.

thanks

anyways, im off to bed so dont be offended if i dont respond quickly.