There once was a BBS tagline that read...
.."Old virus detected - contact your hacker for an update." It seems that malware authors have taken this joke seriously, and are offering subscriptions to website operators that make use of their software. Malware tends to evolve fairly rapidly to get around the cleaner software, which means that sites that deliberately infect web browsers have to keep up to date to keep as many systems as possible infected. Prices tend to start around $66us and climb from there, depending upon how many systems a particular website is able to infect.
It has become apparent that it is possible to not only turn a profit, but make a decent living by packaging exploits and using them to install browser spies, SSL sniffers, and other infectious agents. Seeing as how zero-day exploits can sell for $1kus on up on the black market (unconfirmed reports state that organizations are willing to pay up to $100kus for zero-days in Windows Vista), it's very cost effective to turn around and re-sell use of these exploits. This also has the added effect of advancing the state of the art in malware obfuscation technologies, which exists in the form of encryption, polymorphic code, arbitrary codeblock manipulation, and techniques that the white hats haven't even heard of yet.
The outfits that sell subscriptions to their malware even offer customer and tech support to their customers. One can only wonder when they'll start outsourcing.