I don't understand though how a system could forever be compromised once the infection has been cleaned.
There are no guarantees or shortcuts
when it comes to malware removal, especially when dealing with backdoor Trojans
, Remote Access Trojans
. These types of infections are dangerous
because they not only compromise system integrity
, they have the ability to download even more malicious files. Rootkits can hook into the Windows 32-bit kernel, and patch several APIs to hide new registry keys and files they install. They are used by backdoor Trojans to conceal its presence (hide from view) in order to prevent detection of an attacker's software and make removal more difficult. Remote attackers use backdoors as a means of accessing and taking control of a computer that bypasses security mechanisms. This exploit allows them to steal sensitive information like passwords, personal and financial data which is then sent back to the hacker.
Security vendors that claim to be able to remove rootkits and backdoor Trojans cannot guarantee
that all traces of the malware will be removed as they may not find all the remnants or correct all the damage. This means infections will vary and some will cause more harm to your system than others.
Many experts in the security community believe that once infected with such malware, the best course of action is to wipe the drive clean, reformat
and reinstall the OS. Please read:
Backdoors and What They Mean to You
Whenever a system has been compromised by a backdoor payload, it is impossible to know if or how much the backdoor has been used to affect your system...There are only a few ways to return a compromised system to a confident security configuration. These include:
Reimaging the system
Restoring the entire system using a full system backup from before the backdoor infection
Reformatting and reinstalling the system
This is what Jesper M. Johansson
, Security Program Manager at Microsoft TechNet has to say: Help: I Got Hacked. Now What Do I Do?
The only way to clean a compromised system is to flatten and rebuild. Thats right. If you have a system that has been completely compromised, the only thing you can do is to flatten the system (reformat the system disk) and rebuild it from scratch (reinstall Windows and your applications).