Internet Security key doesn't work after going to Windows 10
I've been using F-Secure Internet Security on my desktop with Windows 7 for a while now, but after upgrading to Windows 10 I couldn't get it to work. I found my product code, so I figured uninstalling the software and installing it again would work. However, even after uninstalling with the official uninstaller, I still can't use my product key, because it is said to be already in use. I'm 100% sure it is the good code and I'm also completely sure that I've uninstalled everything before installing again. Does anybody know how to solve this problem?