Good move on their part, although I'm surprised they weren't able to create something like this in-house. Basically if you crawl every freakin' web page on the internet you pretty much should find all the bad guy's landing pages.
Edit: Plus, per-machine licenses, and profitability -- how much is it worth vs blacklisting manually?
That said, its a great use for the crawler, as long as you are reading web pages to figure out how to index them, might as well scan them for malware. As a marginal cost I expect it to be quite low once you have the crawl infrastructure in place.