Fun Fact: In the days of printing terminals (e.g. Model 33 ASR Teletype), it was not uncommon to be connected to computers via half-duplex circuits. This meant that everything you typed on the keyboard was immediately printed, just like a typewriter. In a situation like this, how do you hide someone's login password, which is just going to be printed on the paper roll possibly just sitting there for everyone to see later. The answer was to black out the paper BEFORE the user entered their password, by typing a series of different characters repeatedly over the same area after the password prompt. The result was a blacked out area of ink as long as the (not very long) maximum passwords lengths. When the user then typed their password, it vanished into the existing ink blob. For terminals that couldn't carriage return without a line feed, this could be accomplished with rapid backspacing. So now you know.