Macamatically Challenged - When your Mac is so confused it thinks you're trying to hack

When your Mac is so confused it thinks you're trying to hack it, just because you tried to open a file from a Windows computer.

My Mac said it was under attack when I tried to open a Word doc from my brother's laptop.

I tried to send a picture, and it asked if I was trying to steal its identity.

My Mac started singing 'Let It Go' when I plugged in a USB from a Windows machine.