Issue: user account maintenant pages are targeted by spammer to create fake account on your site.
To mitigate this issue on top of a solid firewall, you can change the default URL and page name so that the crawler won’t be able to automatically find it.
1-Edit or create a menu item for the Virtuemart USer Account Maintenance page if you didn’t have one previously
2-Set the page title and the alias to whatever you think is more suitable. You might for instance localize the string.