Microsoft's legal team has worked hard to kill "malvertising" and botnets and they've had some great success recently:

The U.S. District Court of Eastern Virginia last week granted a motion that, in effect, gives Microsoft permanent ownership of 276 Web domains once used by the Waledac cybergang to send instructions to hundreds of thousands of spam-spreading PCs.

There's still plenty of work to be done and many other botnets to kill, but this is definitely a great victory for Microsoft's team. [USA Today]