Many kinds of viruses are NOT designed to make their presence obvious.
Maya scene files can contain malicious code that might make Maya unusable at certain dates, until then just infect files in hopes that you will pass them to unaware friends and colleagues. See the Forum section dedicated.to this issue.
MA are open text files, where it is easy to detect any malicious script code, while MB are "compressed" to binary code, where the code is impossible to detect without opening the file.
I'd suggest disabling Automatic Script Execution in File>Open (options), and look for more information over the Net to find out which folders ought to be deleted.
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Maya2019.1 @ Windows10 & GeForce GTX1080Ti
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