Sounds like malware if you were redirected to another webpage. They hide in things called BHO *Browser Helper Object) and you need a Spyware/Malware remover instead of anti-virus software. You need both AV software AND Spyware remover software to cover all your bases.

Spybot is free (just Google it up) and they'll help you step by step on their site if the software alone doesn't do the job.

Just avoid any strange websites... If you surf the web like most people and just click on any link without reservation you're going to get malware. Don't follow email links from strangers either.