Like its rivals, Sony had tried to keep its new PlayStation Portable on a tight leash, installing controls so it couldn't run programs and games not vetted and licensed by the company.
But the PSP, released in the United States in March, has been the target of fervent attempts to unlock its capabilities, which go beyond any previous handheld game machine.
Sony's restrictions were defeated by a program disseminated on the Internet this week. It requires two memory cards, which are switched while the PSP is working.
The exploit may not be practical or safe (an accompanying warning says it could cause damage if done improperly), but it represents a challenge to Sony's policy of tight control and opens the possibility that PSP games could be pirated.
Sony has previously taken a hard line against those who install unauthorized software on its products. In 2001, it went after a Web site that provided software for the Aibo robot dog, saying he was altering their product without a license.
Sony officials did not immediately return requests for comment Wednesday on the latest hack.
The hack works on PSPs with version 1.5 of the "firmware," the equivalent of a computer's operating system. Version 1.5 is the original firmware version for U.S. PSPs, but Sony in May released version 1.51 for users to download. The hack does not work on the updated firmware.
The earliest version the PSP, released late last year in Japan, was hacked several months ago. SOURCE