What's the point of creating new bills with more security measures to prevent counterfeiting? (For example in the USA the new $100 bills have more security features).
If the old bills are still acceptable as currency, why would anyone even try to counterfeit new banknotes with all these security features?
Why don't people counterfeit bills from the 1800s (which are still legal tender - USA) and have NO protection from counterfeiting at all?