HackShield is the current anti-hacking system on the Combat Arms engine. It detects found hacks from previous stages of the game and abruptly shuts down the game on the hacker , it is also known to silently report players via log to Nexon. It is unknown if the shield would work on hacks that weren't blocked by Nexon, that is, if it would report it to Nexon even though it wasn't discovered yet.
HackShield changed its loading screen during the early months of 2009. Instead of showing its trademark "Shield", it now randomly generates one of the second-generation Combat Arms wallpapers that can be obtained on the official Nexon website for Combat Arms.
Some FMs also said that it just detects any type of program which interferes with the Engine launching. That's probably why every type of hacking program is usually detected and reported to Nexon. Lots of cheaters think they can't be busted because they got a new hacking program, but it is not so.