I think I have a virus

I have no idea how it got there, I'm thinking my l3 year old son was viewing web pages and it came from him clicking on certain sites. Thinking he was doing something bad, I went back through all the history, and there wasn't any bad sites he had clicked on , LOL just game cheat sheet web sites for his playstation. Now, this is what happens when I connect to the internet, and start clicking on web sites. A web site comes up, kind of like apop up, says Stop, a big bold stop sign, telling me I might have spyware on my computer, And when I try to click out of it, it won't let me and norton kicks in and says there's malicious script content on this site, and says to get off in so many words LOL I can't remember exactly what it says, so I do, and every time that happens which is twice now, it puts up these icons on my desk top there's 3 icons, on says infamous download, which I suspect is the virus, the other two just say the number 0 under the box. I've deleted these once, and now there here again. I have no idea what's going on, but I have noticed my computer has been real sluggish, acting up, and such the last couple days, ever since my son got on here, I just updated norton and am running a virus check now, it's been going on for 45 min now and still going, Will post back when it's finished. But I don't know where spyware might have come from, I don't do anything on here but go to my garden sites email friends, email pictures, and such,