This type of behaviour can be caused by malware. Try running several malware scanners. It is best to run several as each will pick up things that the others miss. Some scanners you can try are: * Malwarebytes - http://www.malwarebytes.org/mbam.php * SuperAntiSpyware - http://www.superantispyware.com * Ad-Aware - http://www.lavasoft.com/products/ad_aware_free.php * Windows Defender - http://www.microsoft.com/windows/products/winfamily/defender/default.mspx * Spybot S&D - http://www.safer-networking.org/en/home/index.html