Don't Let the FUDs Get You!

Keep in mind that while your antivirus software may detect many types of malware, there are also a great number of malware programs which are 'fully undetectable' or FUD.

Malware may be encrypted so it's not possible for antivirus to scan through it.

Malware developers will check the detectability of their programs using widely used antivirus programs.

Malware can also evade antivirus software by using 'fileless techniques'. This means that the malware will run entirely in RAM - there will be no actual files downloaded to a PC. Rebooting your operating system can clear RAM, but some malware can manipulate the registry or PowerShell to keep functioning. It is also possible for ransomware attacks to work without using any files.

Beware of zero day attacks, that will successfully circumvent antivirus software before the malware is discovered. While virus definition updates are distributed daily, thousands of new malware attacks are also devised each day.