A key-logger is a Terminate and Stay Resident (TRS) program that runs in the background of the OS, logging every keystroke made on the machine its on. Depending on the author of it, they might have changed the code on it to work as a backdoor program and foward all the info it gathers to some site. It is basically used to spy on whoever uses the computer and it compromises the integrity of security.
People place it on computers used in internet cafes or very travelled public places or wherver people are likely to use it with their credit cards, then the program forwards the info and then...
(You get the point..)
A backdoor program comes in many forms, most are used to stay resident and collect information, recieve and forward instructions, or can be instructed to use your system resourses in a concerted attack to a site. (A DoS attack.)
Both have malicious code that basically sets off the warning bells of any anti-virus program because they aggressively utilize memory resources of the computer without valid instructions from
any core component of the OS. (In other words, spawn processes from the memory and have no outlet or parent program to write-back to.)
But you should know what you are getting yourself into if you got a key-logger on your machine, that only mean that you are up to no good anyway....
