How Does Anti virus detects viruses?

The process behind the Anti Virus:

The Antivirus follows two methods to detect the malicious software. They are
>>Virus Dictionary Based Detection
>>Suspicious Activity Detection

Virus Dictionary Based Detection
In this method, Antivirus manage a dictionary file which has the identified virus signatures. Whenever an executable is running, antivirus will check the executable file source code with the dictionary. If the source code match with any virus signature, then antivirus will immediately inform you that the virus is found.
Antivirus will check the executable file whenever file is opened or created or emailed or downloading.

Suspicious Activity Detection
The suspicious activity detection method is more effective than the Dictionary based approach. It can detect even a new virus. Antivirus observes the behavior of the executable file. If the executable file does any illegal process or create any executable file, the antivirus will block the executable file and alert the user