Till yet we don't have much information about the hack, but with the deface message from says that hacker is warning to the HackForums admin about the security.
On the deface page hackers wrote -
"[403 Forbidden Error] - You might be blocked by your IP, Country, or ISP." That's really nasty msg guys , don't u think so?!At the mean time the, when I have check the forum it is unavailable, but by continuously refreshing the page, after some time, site shows the deface page. You can see that forum is still deface. You can also check the mirror of the hack at Zone-h and deface can also view at Google webcache.
Earlier one year ago, another popular hacking forum " Garage4Hacker" has been hacked and defaced. The forum was hacked by the zero-day vulnerability on the vBulletin Forum CMS.
We are trying to extract more information on this hack, and will update this post. So stay tuned with us.