What is it called when someone types a random string of characters in an online conversation? [duplicate]

Is there a name for the action of furiously typing a random string on the keyboard?

keyboard mashing

Keyboard Mashing is, essentially the result of someone mashing their keyboard in certain circumstances. Such as in times of frustration, anger, boredom, an attempt to relieve stress or due to a violent spasm in the typist's hands and arms. This generally occurs in chatrooms or on chat programs, such as MSN, IRC, AIM etc.

RandomMSNnick #1 says: "Hey dude, what've you been up to today?"

RandomMSNnick #2 says: "fghjfghjas da874r"

RandomMSNnick #1 says: "Been that kinda day, huh? Ain't seen you Keyboard Mashing in a while.."

https://www.urbandictionary.com/define.php?term=Keyboard%20Mashing

Also consider:

nonsense

Nonsense is stuff that sounds like language but doesn't have any meaning, like the phrase higgledy-piggledy-po, or fwumphy-doo. The most famous nonsense poem is Lewis Carroll's "Jabberwocky."

Nonsense means exactly what it sounds like: not containing a lick of sense. Nonsense words are made up.

https://www.vocabulary.com/dictionary/nonsense

gibberish

Gibberish is nonsense sounds or writing. A baby's babble is often called gibberish. When someone is speaking a foreign language you don't understand, what they're saying will sound to you like gibberish.

https://www.vocabulary.com/dictionary/gibberish