Security firm Imperva revealed that more than 35000 websites based on vBulletin CMS have been hacked exploiting a known vulnerability.
On August vBullettin authors warned on “Potential vBulletin Exploit (vBulletin 4.1+, vBulletin 5+)”. The exploits vector was found is the installation directories of the above versions, due this reason as a workaround is suggested to delete these folders.