There’s an excellent explanation of “why Cheating-Death is different” on its official web page (http://www.unitedadmins.com/cdeath.php). In short:

Cheating-Death is particularly good because it works from both the client and server side. Servers have the option of requiring clients to run the C-D client software or allowing clients to run without it while marking them as less trustworthy. This flexibility, combined with regular and excellent updates, make Cheating-Death the third-party anticheat utility of choice at the time of writing.

HLGuard ( http://www.unitedadmins.com/hlguard.php ) was once the best anticheat utility around. It’s still one of the few Half-Life tools with current updates. The downloadable server-only version (http://www.unitedadmins.com/hlguard-dl.php) can’t do some of the clever stuff Cheating-Death can, such as preventing cheating or incompatible players from ever joining the server in the first place, but it does stop some of the most obvious wallhacks, aimbots, and other hacks.

There’s also an excellent FAQ (http://docs.unitedadmins.com/hlguard/en/) for the title, which explains some of the neater features, including a Filescan feature to detect modified game files and some good aimbot detection. The latter is especially tricky; like many other systems, it calculates the accuracy of any given player and flags warnings and triggers actions (such as bans) if that player’s aiming skills obviously exceed human capabilities.

Because Half-Life, Counter-Strike, and other Valve products are gradually transitioning over to a more secure framework on their Steam content delivery system, it’s natural that Half-Life creators Valve would eventually make their own in-house anticheat system. This has the distinct advantages of having input from the creators of the game and more concrete punishments for the bad guys, as you can see by the message if you join a VAC-enabled server over Steam:

On the other hand, it’s hard to learn about the actual anticheat mechanisms and which cheats VAC detects, because the update information usually reads “New detections and detection strategies.” That’s very nonspecific when compared to the other, more transparent anticheat systems. On the other hand, while Cheating-Death is more watertight than VAC, it looks like VAC is catching up.

There’s no separate download location for updates to VAC. Steam automatically pushes down the latest fixes and patches automatically. Valve also promises VAC functionality for the forthcoming (at press time) Counter-Strike: Steam, hopefully meaning many more months and years of no cheating.

For example, a good player will know exactly where you are based on the sounds you make throughout the level. Based on those sounds, he can accurately predict your next move. However, this is also characteristic of someone using a wallhack, so what can you do?

For one, someone using a wallhack will spend a lot of time looking at otherwise uninteresting walls. Seeing someone strafing with his face up against a building, for example, should raise your warning flag. In a similar vein, if you see someone make good strategic judgments without ever looking into open space to get his bearings, he may already see open spaces—through the walls!

It’s difficult, but not impossible to identify someone using an auto-aim cheat. Such a player will usually make a series of extremely quick, unfluid movements, too precise or odd to come from a human hand on a mouse or trackball. You may also see him lock onto other characters without first looking in the appropriate direction.

These cheats are never completely accurate, can be ineffective in laggy situations, and may not function well with projectile weapons, so pay attention to a suspect’s choice of weapon. The best weapons for auto-aim use super-swift bullets that reach the target immediately.