What is '@!' file?
Solution 1:
If you use Vim, this could be because you typed :w@! instead of :wq!. On the US layout, @ is on 2, directly above QW, and right next to ! on 1. Easy to mistype.
You can verify this by running Vim again, and examining the command history by either scrolling up using the up arrow key in command mode, or typing q: in normal mode.