1) Virus Definitions:
This is practically the first method of traditional antivirus software to identify malware. These programs rely on signatures to detect new malware. Provided that the company has already analyzed the proper signatures of the file and extracted and placed it in the database. Threats are compared to this database, and your device is protected when it matches the signature.
But while this approach prevents malware from spreading, cybercriminals try to stay one step ahead by writing new types of viruses that do not match the virus definition nor encrypt themselves and modify their code.