Microsoft Antivirus Scanner released - what do you think?

It does sound interesting. I didn't download it, but I did see in the write-up you linked:

Microsoft Safety Scanner does not require any installation, does not offer real-time virus scanning functionality and it does not have the update functionality unlike other anti-virus tools. It weighs up around 70.3MB, and contains up-to-date virus definitions. Once downloaded, the Safety Scanner will expire in 10 days, pushing you to download a different copy to get new virus definitions.

That last part, about expiring in 10 days is troublesome. I suppose in this world of everybody being "always connected" and online-only tools, 10 days is a generous timeframe, but....

Anyway, thanks for bringing this new thing to our attention.

There is nothing in the Microsoft announcement that says the app is portable. Only bloggers are saying it is portable and their definition usually means it will run from a USB stick, nothing more.

This is what you want:

http://www.microsoft.com/en-au/security_essentials/default.aspx

Originally w7/vista, but now on XP.

Nicer (quieter) than AVG/Symantec etc

Use in collaboration with ClamWin.

Microsoft Security Essentials has been around for a while now (and available for Windows XP since it's beginning), but as Depp.Jones states, is in no way Portable; on the other hand Microsoft Safety Scanner has just come out, and according to some may be Portable, that is what this discussion is about.

I did a "Quick scan" (took about 6 mins) and, apart from the usual MS/AV stuff:

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Keys added:1
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HKLM\SOFTWARE\Microsoft\RemovalTools\MSERT

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Files added:1
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C:\WINDOWS\Debug\msert.log

Results Summary:
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No infection found.

Doesn't seem to want to remember that you've agreed to the licence though.

They already have this so why come up with a new one-time tool?