Can a file contain a virus that an antivirus cannot detect? [duplicate]
Suppose that I have an external storage (such as a USB memory stick or an SD card) which contains some files (such as documents or images).
Suppose that I am running an antivirus which scans drives and devices on access, such as Kaspersky Internet Security.
Can potentially malicious code be hidden in a file in the external storage and not be detected by the antivirus?
Or, rephrasing a bit, how much can one trust an antivirus' device scan?
I am aware of the fact that files can contain viruses, as explained in Can a PDF file contain a virus?, in Can .mp4 files contain viruses? [duplicate] and in Virus Encoded in Video, for example.
However, since I do not know how an antivirus scan works, I am interested in understanding if I can "safely" open a file in an external device if my antivirus does not warn me when I plug it in or if I shall perform some additional test.
