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Windows XP users unable to successfully install the operating system's first service pack face a bad choice: an unstable system or a vulnerable one with an extremely serious hole that the newly released SP1 corrects. Now, a software developer has released a freeware tool to block exploits of the previously undisclosed flaw--even without SP1.

The flaw, described on a handful of security message boards and revealed earlier this week, relates to the operation of Windows XP's Help and Support Center's "self healing" function. It could let a malicious cracker delete files by remote access. The exploit could be easily distributed as a URL in an e-mail or on a Web site.

Needed: Fast Fix

Microsoft has fixed myriad such potential hacks through security patches. However, the company chose not to issue a separate patch, and instead fixed this one only in SP1, released last week.

"We concluded that the best way to deliver the fix was via [SP1]. This is in keeping with our long-held conviction that service packs--not patches--are the delivery vehicle of choice for security fixes," says a Microsoft statement posted this week. A Microsoft spokesperson verified the company will not release a separate security patch for that specific bug.

This bug is unique, however, because security researchers consider it to be "trivially easy" to exploit.

"It is such a huge threat--because it is so trivially performed and so devastating to the unwitting user," says Steve Gibson, a security expert and software developer who was one of the first to speak out about the problem.

Gibson has published Xpdite, a free downloadable tool that patches Windows XP without requiring use of SP1.

"It handily removes the vulnerability from any Pre-SP1 XP system by replacing the dangerous script file [in XP] with the safe replacement contained within Service Pack 1," Gibson says.

Users Tell of Upgrade Pains

That is good news for many users who have had problems installing SP1. One user, who contacted PC World, found that after installing SP1 he could no longer switch user identities.

"I found that I could make the problem go away by uninstalling Win XP SP1, but now wonder how I can access the fixes in SP1 that do work," says John Avant of Fort Davis, Texas. He adds, only partly tongue in cheek, "I am praying for Linux."

He is not alone. While most users apparently installed SP-1 successfully, shortly after its posting Internet support forums erupted with user complaints of problems after installing the service pack.

Besides the identity-switching problem, some users say they cannot start their systems without crashing repeatedly. Some couldn't even install SP1, while others describe disappearing screen icons and loss of DSL connectivity. "Will there be a service pack out for the service pack?" quipped one wag on a message board.

Microsoft representatives did not comment on user complaints about installation problems. The company reiterates that upgrading to SP1 is essential to obtain numerous necessary patches and for continued use of Windows XP.

Slow Adopters

Installation problems are keeping some users off SP1, but others are backing off for other reasons. Some businesses do not install service packs immediately upon release, preferring instead to test them to make sure that they won't cause problems.

"I've been hearing from many corporate types who no way will blindly install SP1 after being bitten in the past," Gibson says. "So they are desperate to close this gaping vulnerability immediately and independently of SP1."

Also, many users who still have dial-up Internet access say they don't have the patience to download the file, which can be 137MB at maximum. The "express" installation involves 30MB of code, which takes about 90 minutes to download with a 56-kbps modem connection. In some cases, an ISP will automatically drop lines after an extended download.

Microsoft offers Windows XP SP1 as a free download, and will also send a CD containing the update for $10 plus shipping fees.

Eventually, Windows XP users may have no choice but to battle the gremlins in their own systems if they ever want an operating system upgrade. Microsoft has said all future updates to Windows XP will require that SP1 be installed.

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