Almost by accident David Taylor, a senior information security specialist at the University of Pennsylvania struck up an online conversation with a malicious hacker that went by the name of Diabl0.
Mr Taylor told the BBC News website that the opportunity to chat arose when he investigated a suspected phishing e-mail sent to someone at the University.
When he had compromised a dummy computer with the malicious e-mail he noticed that the machine contacted an IRC chat server making him suspect that it was about to be turned into a zombie.
Once he had extracted the name of the chat server and the channel from the captured network traffic he logged in to try and spot if other university machines had fallen victim.
Mr Taylor noticed someone else in the channel and after a couple of tries had a short conversation with the administrator who went by the name Diabl0.
Although there is no direct evidence that this Diabl0 is the person arrested, Mr Taylor said whoever he talked to connected from a computer based in Morocco.
Mr Taylor has passed all the information he gathered to the FBI.
During the chat, Diabl0 revealed that the Mytob worm had a very sneaky purpose. One of its intentions was to lower security settings on Microsoft's Internet Explorer browser so certain pop-up adverts would not be blocked.
Diabl0 said he would be paid by the pop-up ad makers for every user hit. Even if the compromised users managed to remove the virus, bragged Diabl0, the settings would likely go unchanged and the stream of unwanted adverts would continue.
Every time an ad was sent to a user, Diabl0 would get credited with a click. With Zotob being one of the worst outbreaks of 2005, Diabl0 could have expected a bumper payday.