Apple Inc. has issued a software update that creates problems for iPhones modified to work with a cellular carrier other than AT&T Inc. and disables at least some unofficial programs installed on other iPhone handsets.

Apple warned earlier this week that the iPhone update -- which adds access to the iTunes Wi-Fi Music Store and fixes some security flaws -- could permanently disable phones running programs that untether phones from its exclusive partner's network.

Several gadget enthusiast Web sites, including Gizmodo and Engadget, as well as online postings from hacker communities reported that, depending on which unlocking program was used, certain modified phones no longer worked after they installed Thursday's software update. In some cases, the phones worked, but only with the original SIM card that ties the phone to AT&T.

Some sites also reported uncondoned third-party applications on the iPhones became disabled after the update.

Some hackers had characterized Apple's warning as "a scare tactic." Despite Apple's history of playing cat-and-mouse games with hackers in the past, company officials insisted they were "not proactively" trying to make hacked iPhones useless.

It was unclear how many iPhone owners had unlocked their phones, but the programs -- including several that can be downloaded for free -- appeared to be particularly popular with European consumers. Apple isn't selling the iPhone or initiating the service in Europe until November, so the unlocking software allowed Europeans who bought iPhones in the United States to use the $399 devices.

Installing Apple's latest iPhone update is optional.