A 20-year-old hacker admitted Monday to surreptitiously seizing control of thousands of Internet-connected computers, using the zombie network to serve pop-up ads and renting it to people who mounted attacks on Web sites and sent out spam. Jeanson James Ancheta, of Downey, California, pleaded guilty in Los Angeles federal court to <A HREF="http://www.cnn.com/2006/TECH/internet/01/23/hacker.ap/index.html">four felony charges for crimes,</A> including infecting machines at two U.S. military sites, that earned him more than $61,000, said federal prosecutor James Aquilina. Under a plea agreement, which still must be approved by a judge, Ancheta faces up to 6 years in prison and must pay the federal government restitution. He also will forfeit his profits and a 1993 BMW. Sentencing is scheduled for May 1.