Attack on computer when using google?

Hello everyone. I'm new here and I got little problem. I'm not very handy with computers (just wanted to say that)... So the problem is - I'm getting messages from Norton AntiVirus 2010 when searching with Google that attack on my computer got blocked... It's a bit strange :p (I get messages like this on other, random situations too). Should I just ignore it or is there something wrong? I'm a bit worried... I ran Full scan and found one trojan horse ... But messages didn't stop to pop-up.

 

Can someone tell me what should I do? Is it Norton problem or I have more viruses which I can't find? Thanks