We received a reply from WHMCS this AM and understand the WHMCS Google Payment Gateway Addon hack has affected all versions of WHMCS
Please read Matt's reply below:
"I'm pleased to advise that a patch is now available for this. The full details can be found @ http://forum.whmcs.com/showthread.php?64778
The Google Checkout issue I can confirm does affect all versions.
Any problems or questions, please let me know.