Updates issued on Thursday by Apple did not fully solve problems afflicting some iMacs, and in some cases made the screen-freezing worse, iMac owners have reported.

Apple acknowledged it is again looking into the issue.

The two updates - tagged as 1.2 for Tiger, 1.3 for those who have upgraded to Leopard - are only vaguely described by Apple as "important issue fixes" that affect the 20-inch and 24-inch iMacs introduced three months ago. However, as users who pulled apart the updates Thursday suspected, they were designed to stop the ifreezes that have plagued iMac owners, said Lynn Fox, an Apple 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 lockups 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 lit.

Although some users posting to Apple's support discussions said the update had put a stop to the intermittent lockups, many saw no decrease in the frequency. "Freezing seems the same after installing the 1.3 update," said Paul Verhelst on this thread.

A few even claimed that the update had exacerbated the problem. "I updated and it actually got worse," said James Brancaccio on another thread dedicated to iMac lockups.

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 lockups have never been able to agree on whether the problem is software- or hardware-related; the updates for Tiger and Leopard did not settle the issue, though 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 problem has been a hot topic on the company's support boards. One late August thread includes over 600 messages.

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 their iMac back to Mac OS X 10.4, Tiger.