Two California teenagers pleaded guilty on July 29 to charges that they hacked into several U.S. government computers earlier this year and installed sophisticated programs to intercept passwords on the machines.

In an agreement with federal prosecutors, the 16-year-old boys each pleaded guilty to one count of illegally accessing a government computer and one count of wiretapping. In exchange, prosecutors asked U.S. District Judge Maxine M. Chesney to sentence the boys to probation but did not specify for how long.

The teenagers were suspected of worming their way into at least 11 sensitive computer systems at U.S. military installations and dozens of systems at other government facilities, including federal laboratories that perform nuclear weapons research

The attacks, which occurred in January and February, were characterized by Deputy Defense Secretary John J. Hamre as “the most organized and systematic attack” on U.S. computer networks to be detected by authorities.

As a condition of their probation, the juveniles have agreed to use a computer with a modem only under the supervision of a teacher, employer, or librarian. While on probation, the teenagers also are not permitted to possess a modem at home or to work in the computer field.