Is it just in league? Or is it in every game, even just on the desktop.
Anyways here is what you need to do, ( just in case it is virus-y)
Please download Farbar Recovery Scan Tool (x32) or Farbar Recovery Scan Tool (x64) and save the file to your Desktop.
(
http://www.bleepingcomputer.com/download...can-tool/0
Note: Download and run the version compatible with your system (32 or 64-bit). Download both if you're unsure; only one will run.
Right-Click FRST.exe or FRST64.exe and select Run as Administrator
Click Yes to the disclaimer.
Ensure the Addition.txt box is checked.
Click the Scan button and let the program run.
Upon completion, click OK, then OK on the Addition.txt pop up screen.
Two logs (FRST.txt & Addition.txt) will now be open on your Desktop. Copy the contents of both logs and paste them to pastebin.com. Post the link here.