1. US dollar bills have the largest circulation in the world, so they have become the most forged ones in the world. The anti-counterfeiting technology of US dollar bills is one of the most advanced anti-counterfeiting technologies in the world.
2. Before 1990, the US dollar had no anti-counterfeiting means, because the paper used in the US dollar bill was very unique, and the engraving printing technology of the US dollar was also very unique. The only thing that can be called anti-counterfeiting measures are two special irregular fibers in dollar paper.
The US Treasury Department has said that no matter how the anti-counterfeiting technology is updated, it will not easily change the appearance and feel of the US dollar, including the size of the paper.