http://www.vbulletin.org/forum/showthread.php?t=119663

This little product/plugin disallows automatic sending of spam through the Contact Us page.

Notes to version 1.1.0.0

Due to an almost personal battle against some spammers - intended as: high spam update rate, specially in the weekends when both me and spammers have nothing to do - I added an option to check the allowed number of hyperlinks in the message body, which makes this spam filter a little more intelligent.

The default number of allowed links is set to 12, which appears to be the lower limit from the latest research.

For customizing the message and the number of allowed hyperlinks, an option interface was added, which appears right below the vBulletin Options list - Site Name / URL / Contact Details, as 'Contact Us' Spam Filter Settings.

Version History
1.1.0.2 Additional recognition strings (repetitive 'http://')
1.1.0.1 FIX: Hyperlinks count bug.
1.1.0.0 Additional recognition strings; check of allowed number of hyperlinks in the message body; options interface

1.0.1.10 Additional recognition string
1.0.1.9 Additional recognition string (not published)
1.0.1.8 Additional recognition string (not published)
1.0.1.7 Additional recognition string
1.0.1.6 Additional recognition string (not published)
1.0.1.5 Additional recognition string (not published)
1.0.1.4 Additional recognition string
1.0.1.3 Additional recognition string
1.0.1.2 Additional recognition string
1.0.1.1 Full vBulletin integration, updateable
1.0.0.0 Basic Spam Filter