With every major step in a program's development comes a testing phase, some of which become open to a large user base of testers. Ars Technica reports that "many Windows Live applications are expected to be updated with the roll out of Wave 3, while others will be discontinued. Over the weekend, members of the Butterfly community (MSN/Windows Live testers who have been recognized by Microsoft for their hard work) received invites to participate in 'the next Windows Live beta program' with very limited seats open." [emphasis added] Below is an extract from a Microsoft email, concerning Wave 3 testing:


We do not currently know if this also includes Windows Live Messenger 9. A couple of things suggest it would: M2 has been expected for a while now and this is common method of gaining beta testers for the program. However, the leak of the other day may delay or even stop this beta phase of Windows Live Messenger in fear of another beta being leaked (which it always does when a large amount of testers start using it).

Source: Ars Technica's One Microsoft Way blog