This was in the underneath text on the download site!!
You're too busy to spend a lot of time worrying about protecting your
PC. With Microsoft Security Essentials Beta, you get high-quality
protection against *viruses and spyware*, including Trojans, worms and
other malicious software. And best of all, there are no costs or
annoying subscriptions to keep track of.
You should always download Microsoft software from Microsoft.com.
The reason this download is not available from that source is that the beta
program is closed.
I believe the product will be released soon--the target is second half of
2009, as I recall--so you could just wait for the public release.
I have no reason to believe that the download links posted here are
dangerous--but getting Microsoft software from other than Microsoft links
would be dangerous as a habit.
If you do download from that link, I would recommend going to Help, Upgrade
Microsoft Essentials as the first step after installing.
Microsoft Security Essentials incorporates both antivirus and antispyware
activity--and will disable Windows Defender because it includes the same
functionality and more.