[M. Bison]

Valve employs a technique called delayed bans. You could get banned anywhere from days to months after a single cheating infraction.

As for the possibility of malware, many free cheats come with built-in root kits or rats. The hack developers who take part in this malicious behavior will then typically sell access to your computer as part of a botnet to other blackhats on the internet. Since orangebox is one of the much older games still played, many people who still play use much weaker computers systems hardly capable of maintaining adequate frame rates. This means they're more likely to shut off as many things as possible when playing to boost frame rate and among the things commonly turned off are anti-virus programs. Cheat developers know this and so it's beneficial for them to target these sort of people as they're less likely to be tech savvy and will rarely notice the backdoor running on their system for long periods of time.