When I got started w/ PCs in the late 80s I wrote a GW-BASIC program to take keypresses (one of those 'IF INKEY$<>""' type programs) and write each keypress out to my Okidata dot matrix printer a character at a time. Pressing keys made a physical thing move. That's always fun.
It particularly interesting to send control codes to see what they made the printer do. Pressing <ENTER> got carriage returns without advancing the platen (so you could type over and over again on the same line). <CTRL><L> made the printer advance to the next page of the fan fold. <CTRL><G> made the printer beep.
I figured out that <CTRL><H> moved the print head backward. I used this to make some "impossible to print" output (that is, impossible for my word processor to reproduce because it wouldn't send backspaces for the purposes of over-printing).
Later, during my youthful phase of probing systems on various networks, I ran into systems that, upon entry of a bad password, would send a series of backspaces, various random letters, pound signs, and asterisks before giving a new logon prompt. At the time I didn't put two and two together. (I hadn't yet read Levy's "Hackers" and the idea of using a teletype as an input device on a computer wasn't a thing I'd heard about yet.)
Years later, looking at old captures and seeing this seemingly strange series of characters, I realized what the purpose was. The characters were being sent to obliterate the password printed by your teletype's local echo.
(I want to say the OS was PRIMOS but I don't remember for sure. I saw a number of them on either Tymnet or Telenet-- maybe both.)
It particularly interesting to send control codes to see what they made the printer do. Pressing <ENTER> got carriage returns without advancing the platen (so you could type over and over again on the same line). <CTRL><L> made the printer advance to the next page of the fan fold. <CTRL><G> made the printer beep.
I figured out that <CTRL><H> moved the print head backward. I used this to make some "impossible to print" output (that is, impossible for my word processor to reproduce because it wouldn't send backspaces for the purposes of over-printing).
Later, during my youthful phase of probing systems on various networks, I ran into systems that, upon entry of a bad password, would send a series of backspaces, various random letters, pound signs, and asterisks before giving a new logon prompt. At the time I didn't put two and two together. (I hadn't yet read Levy's "Hackers" and the idea of using a teletype as an input device on a computer wasn't a thing I'd heard about yet.)
Years later, looking at old captures and seeing this seemingly strange series of characters, I realized what the purpose was. The characters were being sent to obliterate the password printed by your teletype's local echo.
(I want to say the OS was PRIMOS but I don't remember for sure. I saw a number of them on either Tymnet or Telenet-- maybe both.)