The AP contacted some of the world's largest electronics manufacturers for details on how they guard against infections — among them Hon Hai Precision Industry Co., which is based in Taiwan and has an iPod factory in China; Singapore-based Flextronics International Ltd.; and Taiwan-based Quanta Computer Inc. and Asustek Computer Inc. All declined comment or did not respond.

The companies whose products were infected in cases reviewed by AP refused to reveal details about the incidents. Of those that confirmed factory infections, all said they had corrected the problems and taken steps to prevent recurrences.

Apple disclosed the most information, saying the virus that infected a small number of video iPods in 2006 came from a PC used to test compatibility with the gadget's software.

Best Buy, the biggest consumer electronics outlet in the U.S., said it pulled its affected China-made frames from the shelves and took "corrective action" against its vendor. But the company declined repeated requests to provide details.

Sam's Club and Target say they are investigating complaints but have not been able to verify their frames were contaminated.

Legal experts say manufacturing infections could become a big headache for retailers that sell infected devices and the companies that make them, if customers can demonstrate they were harmed by the viruses.

"The photo situation is really a cautionary tale — they were just lucky that the virus that got installed happened to be one that didn't do a lot of damage," said Cindy Cohn, legal director for the Electronic Frontier Foundation. "But there's nothing about that situation that means next time the virus won't be a more serious one."