I can't tell you how many PCs I've come across that have all kind of toolbars and crap installed on them. You wonder why people install all of them. They're such a drag on the PC's performance.
Here're a couple of blog posts that explain what's going on. First there's Windows Secrets' article on the latest Java update. Next there's Lifehacker's post on the Digsby instant messaging client.
I won't rehash these stories. Just go read them yourself. And when you install any update or new program, READ EVERY SCREEN and uncheck freely.