It would, in theory, be possible for an emulated game image to contain malware if it can exploit a security flaw in the emulator.
I haven't heard if anybody has ever done that, though.
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Sure, it's possible, but the issue isn't whether it's possible or not, but whether a Windows antivirus can detect that, and the answer is categorical: it can't, because it would have to analyze the code of a script against a specific emulator vulnerability (and we're talking about a very small niche of 8-bit games), and that's not how antivirus programs work in Windows.