Computer users might have trouble when scanning for viruses many times but cannot completely remove them. The symptom has a variety of causes, such as computer's infection of new virus variants, virus' invasion via software vulnerabilities, or improper scanning methods, etc. Among these, the computer's infection of new virus variants is the main explanation.

The new virus variant has similar behavior as an old one which has already been updated in antivirus software's database. For this is the new form, the antivirus software has not got the variant's signature. It just isolates the virus and warns users about the threat, resulting in incomplete disinfection after "repeated virus disinfection attempts".

Viruses now "combine" and "cooperate" to infect computers. Once successfully invading a computer, the "mother" virus will continually download its "offspring" onto the computer. Antivirus softwares, if having signatures of these "offspring" only and lacking signature of the "mother", will consistently disinfect the downloaded "offspring". Consequently, viruses keep existing on the system despite scanning is done time and time again. 

Additionally, there are a number of viruses exploiting operating system's vulnerabilities. If the operating system has not been updated with the patches, the viruses will continually take advantage of these holes to invade the computer without users' interference. Then, if the viruses' signatures have been updated in the antivirus software's database, the software will warn users and disinfect the viruses. However, because the holes on the operating system have not been fixed, the viruses will continue infecting the computer, resulting in the reappearance of viruses after repeated scans. A typical sample of viruses exploiting operating system's flaws is Conficker.

Improper virus scanning also reduces the efficiency of the scan, leading to the incomplete solution to virus problem on the computer. Typically, with file infectors, if users do not scan all the disk drives on the computer, the viruses will be reactivated right after users' running the infected programs on the unscanned disk drives. This means the computer will be re-infected with the same viruses.

To scan and remove virus efficiently, users should follow antivirus software vendor's guides, and update the patches for their operating system regularly. Besides, when having troubles relating to virus (such as viruses' reappearing despite repeated scans, unusual incidents on the computer in spite of finding no virus after scanning, and so on), please contact antivirus  software vendor  to get timely support.

In case your computer has been infected with new variants of virus, or your antivirus software lacks the "mother" virus' signature, your problem will be solved easily with the support from your antivirus software vendor. Specialists will collect the samples of new variants, "mother" virus, etc., and update their software's database with these viruses' signatures. Using this updated antivirus software, you can fully clean viruses from your computer. In other cases, you can get instructions from specialists of your antivirus vendor to solve the virus related problems on your computer.  

If you are using Bkav IS 2011, when encountering any virus related problems or any unusual incidents on your computer, please contact Bkav by following the guide here for timely support.

Bkav