The State Department is recovering from large-scale computer break-ins worldwide over the past several weeks that appeared to target its headquarters and offices dealing with China and North Korea, The Associated Press has learned.

Investigators believe hackers stole sensitive U.S. information and passwords and implanted backdoors in unclassified government computers to allow them to return at will, said U.S. officials familiar with the hacking. These people spoke on condition of anonymity because of the sensitivity of the widespread intrusions and the resulting investigation.

The break-ins and the State Department's emergency response severely limited Internet access at many locations, including some headquarters offices in Washington, these officials said. Internet connections have been restored across nearly all the department since the break-ins were recognized in mid-June.

After the State Department break-ins, many employees were instructed to change their passwords. The department also temporarily disabled a technology known as secure sockets layer, used to transmit encrypted information over the Internet. Hackers can exploit weaknesses in this technology to break into computers, and they can use the same technology to transmit stolen information covertly off a victim's network.