They aren't a search engine really, they look at the pages to see if there are any security problems like viruses etc... I think I could put them in a list of bots to ignore and that would work, but if there are more like them it might be a good idea to have a list for them specifically. At this point Awstats only counts them as one hit for the day (I think) so this isn't a huge problem yet. They load lots of pages so they show up high on some lists. They aren't too abusive right now, one page per minute, but it never ends. If there were 10 of these it could get annoying, I hope they would all get together and share databases somehow.
Browser string: "page_verifier http://www.securecomputing.com/goto/pv"