How can I tell if the login window is fake?

Although a fake login window may look obviously fake, there are ways to recognise it.

Real login windows are browser windows and they work in this way. You can maximise and minimise them and move them to any position on the screen. Fake pop-up windows are bound to the page they are on. They can also move freely and overlay buttons and images, but only within their borders - i.e. within the browser window. They cannot move out of it. This difference should help you spot them.

To check if the login form on the screen is a fake, try the following.

Minimise the browser window in which the form pops up. If the login form that should be in a separate window also disappears, then it is a fake. A real window should remain on the screen.

Try moving the login window outside the border of the parent window. A real window will easily go over; a fake one will get stuck.

If the window with the login form behaves abnormally - it is minimised with another window, stops below the address bar or disappears - it is a fake and you should not enter your credentials.