MyBB Community Forums

I was told that my forum is vulnerable, what can I do to make it safer?

Well, that's a very generic statement from whoever told you that. It could mean anything or nothing, but without knowing more information we can't really help.

What I intend with this topic, is to ask ideas on how to improve security of my forum.

the first and foremost method to protect your forums is by updating it to the latest version, as the MyBB team fixes various vulnerabilities as and when found... you can go through the following Docs/threads to know more about protecting the forums...

http://docs.mybb.com/1.8/administration/...rotection/
http://community.mybb.com/thread-44977.html
http://community.mybb.com/thread-109872.html
http://community.mybb.com/thread-110224.html
http://community.mybb.com/thread-110890.html