A hollow container, fashioned to look like an Eisenhower dollar, is still used today to hide and send messages or film without being detected.

Yu hides messages in cigarette filters, which he then throws on the ground near the beggar.

In the next section, we'll learn about some of the earliest attempts at hiding messages.

It never occurred to me that there might be hidden messages within the text.

It looks like a silver dollar and can be used to hide messages or film.

The backs or shirt and coat buttons were another popular place to hide secret messages.

Often, spies used ordinary things like pencils and coins with hollow spaces to hide messages.

But while people hide messages, other people will always look for ways to discover them.

And increasingly, new tools used to hide messages can quickly be found with a simple Web search.

Still, the mere act of encrypting a message could draw attention, so numerous software programs have been developed to hide messages in other ways.