Camouflage Viruses

You may not heard about Camouflage viruses. It is becacuse, it has never became a threat thanks to the evolution of advanced antivirus scanners. Camouflage viruses are viruses that are capable of infecting a computer by reporting it as a  harmless application to the antivirus software installed in that computer. In the less sophisticated antivirus softwares, the scanning is performed by checking the files for the virus signatures. In such cases, there is a possibility of non-infected files have codes similar to that of the virus codes (a statistical probability) will be notified to the user as virus infected files - a false alarm. This may frighten the user. To avoid this problem, the antivirus softwares implement a logic to ignore a virus signature and not issue alarm under right circumstance.
Eventhough this logic avoid the chances of false alarm, it has opened a door for the virus creators to attempt to camouflage their viruses so that they included the specific characteristics the antivirus softwares were checking for and thus have the antivirus program ignore that particular virus. Fortunately, camouflage virus never became a serious threat, but the possibility existed.
Today, the antivirus scanners are more advanced that they do much more than simply look for a virus signature string. In order to identify the specific virus varient, they not only check for the virus signature, but also even checksum the virus code to identify it. Due to the provision of these cross checks in the antivirus scanner, it would be very difficult for the virus to camouflage itself and spoof the scanner.