This is a payment gateway for Ubercart that implements the "Direct Integration & Protocol Guideline", allowing Ubercart to accept credit card payments via Sage Pay without redirecting the user offsite. It can process 3D-Secure transactions through the "Verified By Visa" and "MasterCard SecureCode" schemes.
3.x is a new release, that's using version 3.00 of the protocol and it adds support for DEFERRED transactions (as well as PAYMENT and AUTHENTICATE as the previous versions).
2.x is the previous version that's using version 2.23 of the protocol. The difference are very little and we encourage everybody to test the new version.
For Drupal 6, use http://drupal.org/project/uc_protx_vsp_direct
Sponsored by Infomagnet.