Background antivirus monitors are most known measure against malware, but they are hardly flawless. Complicated install and need for constant online updates creates openings that malware often exploits.
And creates niche for portable scanners that are easier to get to work and harder to circumvent. ComboFix is anti-malware tool that uses basic and bulletproof techniques.
What it does
ComboFix it relatively small (~3MB) utility. Instead of relying on usual technologies it is basically complex command line script. It implements collection of pre-made fixes for large amount of known malware and hunts down all files associated with it.
- App works purely in console window with occasional message boxes. It asks to close rest of programs and especially other antivirus software so they don't interfere. Official guide says that ComboFix requires Windows recovery console installed locally but recent versions I used make no such request.
- Before actual scan it attempts to creates system restore point and backup registry.
- On run it performs lengthy system scan, with little feedback of current stage. Internet connection and few other things are temporarily disabled and restored later. If needed for virus removal computer is rebooted.
- Upon finishing extensive log file is formed and opened. It has information both on operations performed by ComboFix (like files deleted) and some extras like list of files created in system folders in last month.
- Since criteria for killing files are vague (file name) and process is streamlined (no questions asked) official guide stresses that ComboFix must only be used by qualified person or on request by such person, preferably on one of authorized forums.
ComboFix fix may look primitive and somewhat weird comparing to generic antivirus. However it is brutally efficient. From my experience it had more than once dealt with infections that rendered installed antivirus useless and helpless.
It is not best choice to begin with (I usually suggest CureIt for that) but can be last and only capable measure to save the day.