Its invitation only.
There are steps for you to apply
The Malware Vault forum is now an
INVITATION based forum, and some of the content is limited to the AV-Testers group only (example: Download links for malware samples).
Members can still see the test results for each product, however they cannot reply or create new threads in the Malware Hub.
To join the activity of this forum you will need to contact a
staff member. There is a 30 days trial process to join the AV-Testers group.