How antivirus check any file for virus?

[hitech]

It is really interesting to know how anti virus check any file for virus?

[davo]

i agree its interesting
when i scan i some times stare at every file as there racing along.
i usually know the axact moment when a spyware file is about to pop up.
the only comparison i find, is like the green lines in the movie matrix,
were they dont see the green but everything else instead.
 

[d2]

that davo needs to get off his computer lol