How does a computer virus scan work?

an antivirus has files as virus definition files that look for out for viruses.on scanning these definitions r made use of to search for viruses

SiMple,, It First Of All depends on the type of Antivirus u use,..... the antivirus first searches for file names registered with it ,,,then if it has advanced search ,,it will search within the file codes and find the infected file,,and also scans the active programs..........

i think your question is wrong computer does not scan forthe virus it is antivirus who scans forthe virus ....for scanning you have to install it on the computer first then you have to start for the scan .the mechanism for scanning virus on the computer is that they llok forthe virus signature on the your computer ....... initially anti virus search for the virus signature stores for his record and use that signature find match for the perticular virus if they find then they detect it might delete it from your computer ...or tell you that if it can't be deleted .......

i think when the virus attack in the computer then automatically it start scanning if it is predetermine or pre set to san when some unwanted thing happen and the anti virus software starts scanning the virus i am using avg anti virus and i like it ./..