How does an Antivirus with thousands of signatures scan a file in a very short time? [closed]

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What speed optimization techniques do antiviruses use today to scan a file, provided they have to check for all the signatures + the beh开发者_开发百科avioral scan?

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I'm not a antivirus programmer, but I think the scan engine scans through a file searching for known pattern inside. The greater number of patterns it can identify, the longer it will take to scan.

Optimization maybe similar to database optimization, with patterns indexing.

Identification Methods