As expected Symantec (the makers of Norton, the most popular anti-virus/security suite software) are a tad nervous over Microsoft Security Essentials, and with the number of technology enthusiasts they've scorned over the years they've got every reason to fear a backlash now, so they're upping the FUD campaign from level 1, they're not concerned about MSE, to level 2, stating that its rubbish and won't protect you.

From the BBC:

"Early reviews of the beta are showing that it under-performs when compared to existing freeware products, and well below paid solutions," said security firm Symantec in a statement.

I'm not sure what reviews Symantec are talking about, but I haven't read any data on MSE's performance yet, nor should we expect any for weeks, if not months as that's how long it takes to actual do proper scientific tests.  It does however use the same core engine and definitions as OneCare and Forefront, so the logical thing to do would be to use data evaluating OneCare's performance.

The latest tests by AV-Comparatives, rank OneCare second in detection of new malware, but also importantly it scores the lowest false positives by far, meaning it won't detect genuine files as being malicious.  Which is what led AV Comparatives to award it the highest ranking.  Here's the data for new malware detection rates.  Where's Symantec, oh right down the bottom with a dismal 35%.

Avira AntiVir Premium 69%
Windows Live OneCare 60%
Eset Nod32 56%
BitDefender 50%
AVG Anti-Virus 45%
Avast Professional 42%
Sophos Anti-Virus 37%
Symantec Norton 35%
McAfee VirusScan Plus 25%
F-Secure Anti-Virus 14%

For a good couple of years now OneCare/Forefront has been well above average on detection rates for new malware and on false positives.  MSE using the same engine will continue this trend, and if anything improve it as it will give Microsoft a larger sample size to create new definitions on.

What else do Symantec have to say?

"Referring to Microsoft's basic anti-virus and anti-spyware product as an essential security solution is misleading. Consumers need firewall protection, web protection, anti-spam and identity safeguards"

1) Windows XP SP2, Windows Vista and Windows 7 have a built in firewall which is turned on by default. :-)
2) Internet Explorer 7 and 8, and Firefox and other browsers have web protection, i.e. blacklists of known malicious or phishing/identity-stealing websites. :-)
3) Everyone's e-mail, either web-based like Hotmail or Gmail, or their e-mail clients, Windows Mail, Outlook etc all have built in spam filters nowadays. :-)

Seriously Symantec, you're not doing yourself any favours.  Microsoft Security Essentials is the most non-annoying consumer anti-virus ever, not only that it also has one of the best detection engines out there.