If you are sure about that, maybe there are more reasons to check your PC and the applications available on it, and also make sure there are no hidden applications because most of those malware applications are making themselves hidden, so better run a diagnostic and full scan of your PC. But there are maybe more reasons, like what websites you are accessing; that's one reason for a malware or virus to get through to your PC. Anyway, sorry for the loss. It is regretful because the bitcoin amount is not a joke—11 BTC? That cost a lot, and I can feel how sad and heartbroken you are. If there is a way to recover your loss, I hope you've found it and recovered your loss. Now that you know what to do next, you need to keep your PC containing your assets safer. You should have a separate PC for personal things that could make your assets prone to malicious malware and viruses scattered around the internet.