A man pleaded guilty to charges of launching an attack that hit tens of thousands of computers, including some that belonged to the Department of Defense, and crippled a hospital's network.

Under a plea agreement, Christopher Maxwell, 20, of Vacaville, Calif., will be held responsible for more than $252,000 in restitution to Northwest Hospital and Medical Center and the Department of Defense. He entered the plea in federal court Thursday.

Maxwell and two juvenile co-conspirators were accused of using "botnet" attacks — programs that let hackers infect and control a computer network — to install unwanted Internet advertising software, a job that earned them about $100,000.

Northwest Hospital and Medical Center was attacked in January 2005. Though backup systems prevented patient care from being compromised, prosecutors said operating room doors did not open, doctors' pagers did not work and computers in the intensive care unit shut down.

Investigators later discovered the botnet had also damaged Department of Defense computer systems at the Headquarters 5th Signal Command in Mannheim, Germany, and at the Directorate of Information Management in Fort Carson, Colo.