A critical vulnerability was reported to the VirtueMart team. This vulnerability could be used by a malicious user to easily gain Super-Admin privileges on your website. The bug was patched and the version 2.6.10 (stable version) and 2.9.9b (in RC state) fixes this issue.
Upgrade to the latest version of VirtueMart for Joomla! (this issue was fixed in v2.6.10).