The teenage creator of a botnet who used a clever worm to infect PCs and then steal users' personal data has agreed to a plea deal with federal prosecutors in California.

Jason Michael Milmont, of Cheyenne, Wyoming, is expected to plead guilty to one count of accessing protected computers to conduct fraud.

In return, prosecutors with U.S. District Court for the Central District of California will only press for the "low end" of a potential five-year maximum sentence and US$250,000 fine, according to court documents posted the Web site of Milmont's hometown newspaper.

Milmont's scheme is perhaps most notable for the use of a P-to-P (peer-to-peer) protocol to control his botnet, a technique that makes tracing much more difficult for security analysts and law enforcement.

Milmont created what's known as the Nugache worm. He wrapped the worm into Limewire, a P-to-P file-sharing application, and duped victims into downloading the tampered program.

Once a PC was infected, the Nugache worm would then send spam to everyone on a person's AOL Instant Messenger contacts list. The spam included links to fake Web sites Milmont created mimicking MySpace or the Photobucket photo-sharing site. If a user went to the spoofed site, the user would be asked to download a file.

The file was the Nugache worm, which if downloaded and uncompressed, would then start spamming again. Prosecutors estimate that Milmont's botnet comprised 5,000 to 15,000 computers at a time. The botnet was also used to carry out denial-of-service attacks, including one against an online business in southern California.

But Milmont kept updating the malware. The third version had a keylogging function that was capable of collecting form data from Internet Explorer of the computers he controlled. He then perpetuated identity fraud, collecting credit-card numbers and ordering goods.

Milmont also bought phone numbers with Cheyenne area codes from Skype with pilfered credit-card numbers. Those numbers were used to order goods online, which went to a vacant residence in Cheyenne, federal prosecutors said.

As part of the plea deal, Milmont must pay $73,866.36 in restitution.