The answer to this question is yes.
The reason for doing so is because phpBB2 has been officially retired by the phpBB developers and if there are any security issues that may arise in the last version of phpbb2.0.23 these will not be patched by the developers.
There could of course be other developers out there who will find and issue patches but then you will need to find them in order to secure your phpbb2 board.
So the safest way is to ensure you are running a secure board, is to upgrade to phpBB3 and remain up to date with the latest version at all times.
Related article: http://www.phpbb.com/community/viewtopi ... 4&t=900655.

