A federal judge sentenced former security consultant John Schiefer to 48 months in prison and more than $20,000 in fines and restitution on Wednesday for using hundreds of thousands of infected computers to steal sensitive information from victims and defraud advertisers.

The 27-year-old Los Angeles resident and computer security consultant, who used the online handle "acidstorm," had previously plead guilty to charges of accessing protected computers to conduct fraud, disclosing illegally intercepted electronic communications, wire fraud and bank fraud. Schiefer had admitted that he infected hundreds of thousands of computers in the U.S. and installed keylogging software to record victim's usernames and passwords.

"Schiefer is the first person in the nation to plead guilty to wiretapping charges in connection with the use of botnets," the U.S. Attorney's Office for the Central District of California said in a statement.

The conviction ends an investigation involving the FBI that began in 2005 and which became part of a collection of law-enforcement investigations dubbed "Operation Bot Roast II." In 2007, another security researcher, Max Ray "Max Vision" Butler, was charged with allegedly running an identity theft ring.

In addition to his four-year prison sentence, Schiefer was fined $2,500 and must repay $20,000 to a Dutch advertising firm, which had paid him a commission for adware that he installed on infected computers.

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