Yeah they did ask me about how it may have happened, I don't usually download games on that account since it's meant for uploading, and any games I do download are usually well-known and are verified to be safe. One incident that I can only think though, is when at some point, Windows Defender constantly said there were threats found but after opening Security Center, it said everything was OK, nothing even in quarantine.
So you assume it might have been an infected download. But no scan afterwards showed anything. You did try other scanners, did you? I know that some malware deletes itself after stealing things, as to not get detected. But worst case would be, that you currently have a full suite of root kit and keylogger installed and your machine is part of a bot net.
Also, as long as you do not log out with your uploading account, any cookie and password stealing attack will not care with wich acccount you download and install things. This stuff is scary, and I would hope that the OS and browsers would provide more means of securing against this type of attacks.
