After a quick google search, the common issue appears to be this..:
"It appears to be a browser hijacker for click through ads. Basically someone keeps redirecting you to their webpages so they can generate pay per click revenue. Very Common.
Reset your homepage to Yahoo.
Download and install SPybot Search and Destroy from link below. When installing turn on system setting protection and tea timer. These should prevent hijacking and will let you know when your homepage is changed. Download all updates, disconnect from the net and do a full scan. It should find your hijacker."http://www.safer-networking.org/index2.html
I'm not really an expert, but it sounds like the problem your having.