Juridan is right. machines like these would make excellebt zombies in a ddos or similar distributed attacks, so being a little paranoid is ok. Maybe my response was a bit harsh. But in reality, the chances this was a legit attack are very low. Sure it could be a warning sign that his computer has been compromised and someone took the saved password from his machine and is logging on his in in an elaborate attempt to do some social engineering with the name and it would not trace back to the thief. Or they could just be doing it to mess with him and show they got his info.

so if you are worried take the appropriate steps mentioned above. Scan your computer for viruses/other malware THEN change your password for every single program/website/computer you access. then go ahead and get a new IP from your ISP even if it is DHCP they will usualy stay the same for some time. You may also want to go ahead and check all your banking statements and alert you bank to be on the look out for possible identity theft. Also inform your employer of possible data leaks if you have done work from home. Oh and let any friends that have used your computer to log into their eails to have their info changed as well. this should give you the reassurance that everything will be ok.