Forgery has been a threat for centuries. Every document bearing an intrinsic value is quickly recognized by counterfeiters as providing a lucrative target.
Early societies (14th Century ) enacted severe penalties for forgery.
Forgery was a hanging offense in England.
From 1697 to 1832, 600 counterfeiters were condemned to death.

The threat of severe punishment did not and will not eliminate counterfeiting.

Counterfeiters do not have to make an exact copy, but only one good enough to pass and circulate.

This led to the use of a variety of printing methods not commercially used: Unique modules not available to the general public, distinctive image, designs and patterns difficult to duplicate.
It's simply a combination of techniques to incorporate security features in a document.