Techies at Microsoft Corp. have been working double time this week trying to make sure that customers can still get to needed software patches despite the coming of the Blaster worm's Distributed Denial-of-Service (DDoS) attack.

The attack, which is expected to start tonight, is aimed at Microsoft's Web site -- the site users have been sent to for the patch that will ward off the Blaster worm. Microsoft execs want to make sure that system patching continues even after the attack begins.

''we've been working nonstop to make sure we can provide the patch to our customers and we think we'll be able to,'' says Stephen Toulouse, a security program manager in Microsoft's Security Response Center. ''Our number one concern is getting customers the patch and making sure they can get to our site.''

To that end, Toulouse says Microsoft is guiding users to the patch through an alternate route. Customers can get to it by going to That site won't be affected even if the site goes offline during an attack.

Toulouse adds that they've taken steps to ward off the attack and keep the site up and running, but he would not give specifics for fear that the information would help future virus writers.

He adds that even though Microsoft is frequently the target of DDoS attacks and has practice guarding against them, he can't be sure the site won't experience problems once the Blaster attack hits full force.

''Denial-of-Service attacks tend to be successful because they're brute force attacks,'' says Toulouse. ''It's always one of those things where we'll know when it happens.''

Microsoft has logged an increase in traffic to the site over the past several hours, Toulouse says, adding that some customers had their computer clocks misconfigured so their DoS attacks came early. But he expects to see the traffic flow to the site increase steadily over the course of the day today and tomorrow.

''We've just been preparing as if it's going to start any moment,'' says Toulouse.

The Blaster worm was first detected on Monday. It quickly spread from machine to machine across the globe through a flaw in the Windows operating system. But the worm doesn't carry a destructive payload, only causing a small percentage of infected computers to reboot because of a flaw in its own coding.

Instead, Blaster, otherwise known as LovSan and Poza, is specifically aimed at causing trouble for Microsoft. The worm is geared to harvest as many vulnerable systems as possible and launch a DDoS attack on the Web site starting late Friday or early Saturday morning. By focusing all the net congestion on that Web site, the author of the worm is deliberately trying to make it difficult for IT managers and individual users to download the patch they need to secure their systems against the worm.

Several anti-virus and security companies, including Symantec Corp., raised the worm's threat level to their second-highest rating earlier this week, despite the fact that the number of new infections had leveled off or even slowed. Blaster has not caused much network congestion and hasn't affected Internet traffic on anything but a very localized scale.

But analysts say it's the potential they're worried about.

Blaster exploits a flaw with the Remote Procedure Call (RPC) process, which controls activities such as file sharing. The flaw enables the attacker to gain full access to the system. The vulnerability itself, which affects Windows NT, Windows 2000, Windows 2003 and Windows XP machines, affects both servers and desktops, expanding the reach of any exploit that takes advantage of it.

Where the vulnerability affects servers and desktops in such popular operating systems, there are potentially millions of vulnerable computers out there right now. The security industry sent out a widespread warning about two weeks ago, spurring many companies to install the necessary patch, which was available from Microsoft almost a month ago.

And with millions of systems still unpatched, Microsoft is determined to make sure customers are able to get onto their Web site and download the needed fix.