Hi

Why phpbb is being hacked?.Why there is no security mesaures in the same?.did they released a new one having better security ??

It's the Microsoft effect, when some code is popular people are more likely to go looking for exploits in it and due to the size of the people working on it, it takes a while for the issues to be fixed.

PHPBB has nothing wrong with it, just it's so popular people go looking for bugs/exploits in it. There is also the issue of the people using it, if the person using the code is a dumbass it's more likely to be hacked (for example letting any old file into the server, giving out important details of the database, not getting the code up to date etc could pose a possible problem).

high popularity + open source code = exploits

just keep up with the updates and take all security measures and you should be fine. i ran a high-traffic phpBB site for quite some time without any issues