Is it necessary to have an internet connection to run and properly scan an android device for viruses or malware using an anti-virus app? How an anti-virus app scan an android device for infected files and viruses?
You need an internet connection to download it and for it to update its threats database. Apart from that, you don't really need internet access to have it scan your device. As for how it works, each anti-virus has a threat database which uses to scan files for malicious signatures. Some more advanced will also look for abnormal behavior in the execution of an app, like network connections, root attempts etc.