ValidClick?

Today I saw this on my PPC tracking:

It caught my eye because it came with broken URL parameters. I check out the URL that drove these guys to my site and its starts with http://feed.validclick.com/monitor.php?key=tag-

What is this? I went to http://www.validclick.com/ and started reading… I’m trying to understand what these folks do… and why they’re driving traffic to my site – even if it was just one visitor – its coming with all sorts of tags, including an affiliate ID. Is someone re-selling my ads?