It is always sensible in this situation to run a check for malware
I recommend that you run Disk CleanUp or cCleaner to remove temporary files as this will reduce scanning times by security software.
Boot the computer to safe mode with networking and download and install Malwarebytes (freeware version for home users only), update definitions and run in normal mode. Disable other security software whilst you are doing scans.
http://www.computerhope.com/issues/chsafe.htm
http://www.malwarebytes.org/products/malwarebytes_free
Please download and run ADWCleaner:
http://www.bleepingcomputer.com/download/adwcleaner/