IM Worms in 2006

I've written about IM worms in the past, and even went so far as to write a paper for work (internal-only distribution, sorry about that) where I went on to state that 2006 was shaping up to be the year of the IM worm. 2005 saw a flurry of IM worm families, and a lot more bots were including IM capabilities. The methods remained the same, namely link spamming.

And yet we haven't seen an explosion of IM worms. I don't know why, to be honest with you, all of the evidence suggested that attackers were picking that up dramatically. This does discount the Rbot/SpyBot/etc families using an AIM or MSN Messenger vector (in addition to their other vectors) to propagate, I'm focusing specifically on IM-specific worms. Why wasn't 2006 the year of the IM worm? We saw some, but it ddn't become a huge problem, and we didn't hear about massive network outages due to the IM worm problem like we did in 2005.

This is all prompted by The IM worms armada, posted on the Kaspersky AV weblog:

We've noticed an increase in the prevalence of Y!/MSN-aware worms. These rely on various social engineering tricks to lure the user into a malicious website.

We saw some reactions from the MSN Messenger network operators when they began blocking .pif links, which helped slow down some of the common links being spammed. It had a problem (case sensitivity), but it shows that they're trying to deal with the problem. Could this have cut down on the flurry of IM worms in 06?