. my dad has just had this happen to him, Definately Change your password. i would suggest also doing a good thorough virus/malware scan of your entire PC. to make sure someone hasnt gotten your password that way ie keylogger or trojan. also try to make your password as hard as possible, if possible include besides small letters, Capitals, Numbers and symbols. it is also recommended that you change your pass regularly. maybe 30-60 or 90 days.
btw if you do get a psitive while doing your scan, dont forget that after you remedy the problem to change your pass again right away just in case. only if you get infections or alerts while doing the scan. some say its best to do more than one scan with different brands of scanners for best results. many are free online. I also would like to know more about this if anyone knows. is it a virus? well, hope this helps some..