Can M4A audio files contain a virus or any kind of malware? I think that MP3 can not, and I think that WMA can connect you to a bad site. So, what about M4A? Thank you! 
Mp3 files can be hacked to exploit the media player I believe.
In most cases it isn’t the media file that is infected but hacked to take advantage of a vulnerability in your media player so it is important to keep it fully up to date. The same is true of the WMA format where the file is hacked to tra and exploit the player.
I had never heard of m4a audio files before until I did some googling ;D and I would have thought that since they are a relatively new format it wouldn’t be receiving the same attention as the more popular formats.
Files in .M4A format are actually the audio layer of (non-video) MPEG 4 movies. M4A is slated to become the new standard for audio file compression. This format is also known as Apple Lossless, Apple Lossless Encoder, or ALE. It is a new codec designed to provide lossless encoding in less storage space.