This had been known on past years on that copy-board virus where you would paste up another address instead of yours when you do make transactions because if you do talk on privatekey stealing then this would really talk about keylogger or any malware that do copy and sent out any private keys that he detects in.This would be a lesson learned on your part which you should not carelessly download any files on the net without having any caution because anytime our pc can really be affected which on result to compromise our important informations such as keys or any other similar thing.