Do you have saved email server password in browser and you was logged in to bitstamp web site at moment this happend?
If yes, it could be some virus/malware app, if not, your passwords could be stolen.

Check Qt Bitcoin Trader app properties, if there present digital signature (julyighor@gmail.com), it is legit app, so you don't need to remove it.
But if you installed it using some "Installers", not just copying file, this means you used fake installer witch may contains virus.

You should try remember where you downloaded Qt Bitcoin Trader. If it was official source this means you download other malware apps.
Anyway check all system by antivirus and change passwords in all important websites.
And don't use same password to every web site.