With plus, jj2 is technically much more secure than it used to be before. It has patched many of the networking buffer overflows (several critical security flaws). In the past these were merely exploited to the point where they caused a server to crash, but could have easily been used to execute arbitrary code on a remote machine to compromise it. While many of the well-known flaws have been removed, there are still some not so well-known bugs that need to be addressed.