WoltLab Burning Board 3.x.x PM Delete Cross-Site Request Forgery Vulnerability by NBBN. Founded: 25 December 2007
Examples: http://domain.tld/wbb3/index.php?page=PM&action=delete&pmID=[pmid] http://domain.tld/wbb3/index.php?page=PM&action=delete&pmID=1
Wait for a fix. Or never surf in other sites, if you have autologin on and don't click links, when you are logged in.
I tested it only on 3.0.1 but I think that all version of 3 are vuln.