The virus is being considered by most Garry’s Mod players as a warning from an intrepid hacker. Instead of the spamming function that uses a player’s Steam friends list, a dangerous or malevolent virus could be put in its place, potentially with the power to break systems and computers.
For now, however, the ‘cough’ virus will simply spam the word “cough” to your friends list. This has led many to dub the hacker a ‘white-hat’, or someone who hacks to expose flaws, rather than for malicious reasons.
The virus works by forcing players to download a .dll file upon entering a server. If that ‘infected’ player then leaves that player to join a ‘clean’ server, that previously uncorrupted server will begin forcing players to download the .dll, causing the virus to be ‘contagious’.
Here is a video of the virus in action:
It seems that Garry Newman and his team took the hacker’s ‘warning’ on board, as the exploit was fixed almost as soon as it began.