[zb]

The ink ribbon contains a record of every word you type, and I believe hoovering them up was a common espionage tactic back in the day.

[beala]

It's not uncommon for used typewriters on ebay to include the old ribbon, along with the last fifty thousand characters the previous owner typed...

[PopAlongKid]

Certainly that would be the case with film ribbons, but I don't see how typed character history could be obtained from a cloth/cotton ribbon, especially since they were as I recall reversible (would spool one dirction, then the other when reaching the end), meaning the previous typing would be overwritten multiple times.