Ths is due to a mistype by Microsoft when inserting the link. You are NOT infected. Microsoft website is NOT infected. It is just a mistype by a Microsoft employee.
Microsoft have fixed the link on the windows update page and partially have on the history page on your computer. It looks like some of the regional Microsoft update servers are still giving a cached copy of the update with the bad link, but others are giving the correct link.
The correct link for support or information about this update is
http://support.microsoft.com/kb/2505438
The mistyped link was

http://support.micrososft.com/kb/2505438

Note the extra S in microsft
It is an easy typing error to make.
So Don’t panic about it. I repeat again you are not infected, Microsoft website is not infected, it was just a simple typing error that has been partially corrected and I expect to be fully corrected very soon.

We often see major problems with typo squatting. This is when unscrupulous people buy up every possible combination of mistypes for common domain names, in the hope that they will get money someone mistypes a URL ( web address) and lands on their site/landing page instead. This time it is only harmless advertising but in many cases the unscrupulous owner will either attempt to sell you a fake program or even worse install malware from the fake page.
Watch links you follow & make sure that they are spelled correctly
See the screenshots

Mistyped url on update history for KB2505438

Mistyped URL for KB2505438 from Windows update site

Once again we need to warn you about a scam involving Microsoft Security Essentials
Security Essentials is a free Antivirus program from Microsoft available to any windows user with a validated copy of a supported desktop version of windows ( XP SP3, Vista SP2 Windows 7 ) You should only download it from the Microsoft Security Essentials website
The scammers have created a look a like site with links to download Security Essentials BUT following the links you have to create a membership with them & pay for the privilege of downloading free software. It is the same scam that I told you about in this post about Adobe Reader
This one appears to be a different bunch of scammers but with the same result. They will clear your credit card & sell all your details to anyone they can.
One malware researcher used their links to download Security Essentials & got a nasty trojan instead of the genuine program

Fake Microsoft Security Essentials site

If you read carefully, you see they do say in the tiny small print that MSE is a free program and you are paying for the benefit and convenience of downloading it from them instead of the approved free Microsoft site

We stress again that http://securityessentials-2011.com is a scam site that is trying to steal your money and is not to be trusted . Only download Microsoft Security Essentials direct from Microsoft

The full version of the Microsoft Security Bulletin Advance Notification for this release can be found at  http://www.microsoft.com/technet/security/bulletin/ms10-jan.mspx.

These have a @live.com email address with what at first glance looks like it could be a proper microsoft or MSN email address ( they of course are not genuine Microsoft or associated with Microsoft in any way)

DO NOT fall for the scam & try to ring the 070240****** number . it is a premium rate number that will have along recorded message on it and cost you £0.50 per minute

You won’t get any money from these scammers but they will get money from you

I have blanked out the full email address and phone number from the image to save the unwary