Gdant, thank you for sharing your (dual booted) Windows 7 and Windows 8.1 configuration with us.
I agree with exterminator20.
On demand scanners are light, and when used as secondary scanners, they are often known to catch and isolate malware as well as other infections such as Trojans & (potentially) unwanted programs that traditional anti-viruses can miss on ocassion.
It doesn't hurt.
Try Malwarebytes Anti-Malware. There is a free version which I use, and they've a paid version you can try free for 30 days.
Update: A favorite password manager used by many MT members including myself is called LastPass.
It makes life both easier and more secure by utilyzing encryption security as well as filling in fields (anti-keylogging) and providing, essentially, an additional and secure book marks storage known as The Vault!