From the Stars and Stripes:

Thanks to an increase in counterfeiting of South Korean bank notes, get ready for South Korean paper money that looks different from what you may be used to.

The South Korean government announced recently it would begin issuing newly designed 10,000-won and 1,000-won notes Monday. It already had issued new 5,000-won notes Jan. 2.

But you’ll still be able to use the old money — worth about $10 and $1.

The government is taking the action to thwart what Bank of Korea officials said is a recent increase in counterfeiting, especially of 5,000-won notes.

Those fakes often were a sophisticated product not easily detectable to the unaided eye, bank officials said.

Any guesses who is behind the counterfeiting?  I guess when rigorous sanctions make counterfeiting US currency less appealing, you might as well counterfeit the currency of the nation you know will do nothing towards you about it.