F-Secure is warning about ads for a “leaked version” of Windows Messenger 8 beta. There is no public beta of this and it is a virus.
If you download and run BETA8WEBINSTALL.EXE, you won’t get a new chat client. Instead, your existing MSN Messenger will start to send download links to everyone in your contact list. It also connects your machine to a botnet server.
The download link always contains the recipients’ email address. For example, if you’d have a friend with email address email@example.com, he would get a download link like firstname.lastname@example.org.