You probably should first make sure you have UAC enabled.Here is where to adjust and or enable UAC in Widows 8.1
Go to Control Panel > User Accounts and Family Safety > User Accounts
Click the Change User Account Control settings
The User Account Control Settings window will appear on the screen
On the left, you will see a slider, which controls UAC settings. It has four choices:
Never Notify - no security
Notify me only when apps try to make changes to my computer (don't dim my desktop) because the screen is not dimmed there is a potential security hole
Notify me only when apps try to make changes to my computer (default)
Always notify me - most secure and a bit annoying to some
I would suggest at least default setting but I would recommend "Always Notify"
I would suggest an Antivirus program such as Avast.It is free and you can scan your PC to see if you have anything,since you aren't sure whether or not you might be infected
Then you should scan your system with a couple on demand scanners such as Malwarebytes Antimalware,ESET Online scanner and or Emsisoft Emergency Kit or Hitman Pro.You should keep a few on demand scanners and keep them updated
If something shows up on a scan post here
http://malwaretips.com/forums/malware-removal-assistance.10/
There are more suggestions such as a Backup solution,different Browsers & extensions adding CCleaner if you do not have it installed already as well as a password manager such as LastPass.I think the first suugesstions above are more pressing at the moment
