Apple's latest set of software patches did not fully solve lock-up problems for some iMacs, and in some cases made the screen-freezing worse, according to Mac owners.

Apple said it is again looking into the issue.

Updates 1.2 for Tiger and 1.3 for Leopard are only vaguely described by Apple as "important issue fixes" that affect the 20-inch and 24-inch iMac models introduced three months ago. However, as users who pulled apart the updates suspected, they were designed to stop the lock-ups that have plagued iMac owners, said Lynn Fox, a company spokeswoman.

"Yes, they address the iMac screen freezing issue," Fox said. "We encourage all users to apply the fixes."

In early October, Apple acknowledged the lock-ups and said it was working on a software update that would be released "as soon as we can - most likely later this month." Common characteristics of the freezing included inactive mouse and keyboard; continued background processing, such as music that keeps playing; and the need for a reboot even though the screen remains lighted.

Although some users posting to Apple's support discussions said the update had put a stop to the intermittent lock-ups, many saw no decrease in the frequency. "Freezing seems the same after installing the 1.3 update," wrote user Paul Verhelst.

A few even claimed that the update had exacerbated the problem. "I updated and it actually got worse," wrote another user, James Brancaccio.

When asked if Apple is aware of the reports that the updates haven't stopped screen-freezing, Fox said: "We are looking into it."

Users experiencing lock-ups have never been able to agree on whether the problem is in the software or hardware, and the latest updates did not settle the issue.

Some users actually felt vindicated when the patches didn't end the story. "This underlines my assumption of a hardware issue - the iMac update 1.3 that I just installed doesn't help at all," said a user identified as tmo zoidberg. Fox declined to speculate about whether the freezes might be caused by something other than a software bug.

The lock-up problem has been a hot topic on Apple's support boards. One thread started in late August includes more than 600 messages and has been viewed more than 33,000 times.

Last month, Apple tentatively fingered a mid-September iMac update, pegged as 1.1, for the problem. Previously, some users have said they were able to stop the lockups by rolling back Mac OS X 10.4, a.k.a Tiger, to their machine's original configuration.

Thursday's updates to Tiger and Leopard can be downloaded and installed using the Software Update mechanism built into Mac OS X.