Computerworld — Mac users have reported an unusual number of problems installing Mac OS X 10.5.7, the huge security and feature update that Apple unveiled yesterday.

According to messages posted on Apple's support forum, some users have had trouble downloading the update, while others have seen their Macs hang with a blue screen during installation. While most Computerworld staffers who use Macs reported no issues with 10.5.7, one editor went through three downloads before it successfully completed, while a reporter received the same message yesterday that several users said they'd seen.

"I've made three [download] attempts, and every one of them has failed with an error message telling me that the digital signature for the package is incorrect, suggesting that it may have been tampered with since being signed," a user identified as "jposner" said Tuesday shortly after Apple unveiled the update. Other users confirmed seeing the same message.

Users who were able to download the 442MB update watched as their Macs stalled during its installation. "I just installed 10.5.7 on two machines ... in both cases, after the installation the computer went into some sort of a loop with a blank blue screen," said a user labeled "Lazarus Long" in another support forum thread yesterday. "I finally had to shut down hard and then wait for two or three reboots until I could login." Dozens of other users reported the same problem on the thread.

Still others reported missing external disk drives and disappearing display resolutions. "After updating to 10.5.7 on my Mac mini, my monitor is not recognized correctly any more!" said "cizko" in yet another long complaint thread. "It should be running at 1920 x 1200 native resolution but is now stuck on a bizarre 1920 x 1080."

The MacFixIt site, which closely tracks problems with Apple's updates, posted recommended steps for several of the snafus. For example, it urged users to download the Combo Update -- a much larger 729MB file -- rather than using Software Update to avoid the incorrect digital signature problem.

MacFixIt also culled recommendations from the Apple support forum for the blue screen and display resolution issues, advising that users boot into Safe Mode or step through a five-step process for the former, and that users try a PRAM reset for the latter.

Some users were furious over the difficulties the update posed. "That had to be the worst OS update from Apple I've installed over the last 5 years," said "Seanrobrien" on a support thread.

Another user concurred. "I've been using [Mac OS] X since 10.0.3 in what, 2001, and this was the worst update I'VE seen," agreed "The Dude Abides."

The 10.5.7 update wasn't the first to stymie users. In December, after Apple rolled out the Mac OS X 10.5.6 update, it acknowledged installation problems, and pinned responsibility on partially-downloaded updates.

At the time, one user called the 10.5.6 update a "nightmare" and said it was more frustrating than any Windows update he'd done in the past.

Apple was not immediately available for comment today.