MyBB, formerly MyBBoard and originally MyBulletinBoard, is a free and open source forum software which is developed by the MyBB Group. It is written in PHP, supports MySQL, PostgreSQL and SQLite as database systems and, in addition, has database failover support. It is available in multiple languages and is licensed under the LGPL.

MyBB has a relatively low-risk security record. In August 2008, MyBB performed a security audit (provided by GulfTech) which led to the release of MyBB 1.4.2 on 17 September 2008.

The MyBB Group put security first, giving it the highest priority, to the extent that the MyBB website has a "Security Hall of Fame" to recognise those who responsibly disclose vulnerabilities in the software.

In October 2011, MyBB found 3rd party code had contaminated the 1.6.4 release files. This code could be exploited to open a security vulnerability on a forum running the affected version. It was later found that a security flaw in the custom CMS mybb.com uses to power its website allowed a malicious user to alter the download files to include their own code.

As a result of the intrusion, the MyBB Group now hosts downloads via GitHub to ensure the security of a release. A Forum Security section on the MyBB Community Forums opened in 2011 to provide support for users who have been a victim of an exploit.

Throughout 2011, automated registrations caused forum spam in many MyBB powered forums. In MyBB 1.6.5, released on 25 November 2011, additional methods were added to help administrators locate spam users and manage them effectively as well as providing standard reCAPTCHA support.

In May 2012, hacktivist group UGNazi gained unauthorized control over the MyBB.com domain name using a social engineering technique. The attack appears to have been motivated by the use of the MyBB software by a third-party website, HackForums

MyBB has a 9.6 out of ten review at forum-software.org and was named the best free forum software of 2008, 2010, 2011 and 2012 by the same site. It has a 4.33 out of 5 review at HotScripts, and has been recommended by cloud computing company Standing Cloud. It has been featured in magazines such as The H and runs several sizeable forums on the web, including HackForums, CSNbbs, and several EA Sports boards