"It's absolutely not clear to me (and I don't think anyone) that a focused investment in, say, textbook development is actually going to result in predictable payoff in a transformatively larger number of sustainable content contributors. That doesn't mean that there isn't a potential for such an investment to be successful, and it doesn't mean that it's not a risk worth taking." -- Erik Moeller, Deputy Director, Wikimedia Foundation

http://lists.wikimedia.org/pipermail/foundation-l/2010-October/061608.html

Windows Update issued an update to the Malicious Software Removal Tool which cleaned computers infected by the Storm Worm. Citation here. So, you've got malware that sends out spam and DDoSes PCs, and "malware" that may install a desktop search update depending on the configuration of WSUS. I personally see the former as the bigger problem.