Takedowns of Zeus botnet command and control servers like the one executed last week by Microsoft and others do reduce the criminal activity they spawn - for a while - but attackers learn from the experience and come back with more sophisticated techniques, a security expert says.

Microsoft won court permission to seize servers Friday that took down a deployment of the Zeus botnet, and it even detailed the corporate structure that enabled using the zombie network to steal cash from victims.

The Zeus botnet is now using an unpatched flaw in Adobe's PDF document format to infect users with malicious code, security researchers said today.

Last week FBI Director Robert Mueller called the fight against hackers "the cyber equivalent of cat-and-mouse." On Wednesday security experts trying to take down the Zeus botnet got a taste of what he meant.

Internet service providers linked to the notorious Zeus botnet have been taken down, knocking out a third of the command-and-control servers that run the network of hacked machines.