Counterfeit money has been around for nearly as long as the real deal. When the first coins were minted several thousand years ago, the value of the coin was based on the intrinsic value of the metal. Counterfeiters would scrape off small amounts of precious metal from legitimate coins and use it to cover a cheap base metal and pass it off as a higher value coin. Since then, counterfeit money has evolved into a huge black market, with an estimate of over $200 million circulating the U.S. at any time.

1. TWENTIES AND HUNDREDS ARE THE MOST COUNTERFEITED AMERICAN BILLS.

According to a 2013 Reuters report, $20 bills are the most common counterfeited bills in the United States, but internationally, it's all about the Benjamins due to the bill's broad circulation. To fight counterfeiting, U.S. bills are designed with a number of security features to verify their authenticity: Watermarks that can be seen when the bill is held up to the light; security threads that can be seen when held up to an ultraviolet light (on counterfeits, they appear as a thin line); color-shifting ink; raised printing; and more. A redesigned version of the $100 bill, which took a decade to create and was released the same year as the Reuters report, featured two security features new to that bill: a 3D security ribbon with images of bells and 100s on it, and a color-changing bell in an inkwell. 

2. YOU CAN GET THEM FROM BANKS.

You might imagine that bank employees would be the best at spotting fake money, but on occasion, even they pass on counterfeit bills. When William Hagman, a retired history teacher, withdrew withdraw $2500 in $50s and $100s from his Denville, New Jersey TD Bank account in 2012, he—and the bank—had no idea that one of the bills wasn't legit. Hagman got that nasty surprise when he tried to deposit the money into his Bank of America account. One of the $100 bills was counterfeit, the bank told him, and they couldn't deposit it. After filling out forms, Hagman found himself back at TD Bank to ask for a new, legit bill—but while the bank's supervisor admitted their mistake in handing him the forged note, she wouldn't exchange it because of bank policy.

redditor reported a similar situation in 2015, this time with a Chase bank—and, as in Hagman's incident, the bank wouldn't replace the bill. When a customer leaves the bank, the money becomes his or her property, and banks have no way of knowing what the customer does with the money once they leave the premises. To protect themselves against people who might abuse fake cash refunds, many banks have strict policies on refunding bills—which is why it's a good idea to examine notes before you leave the building.

3. TECHNOLOGY IS HELPING COUNTERFEITERS MAKE MORE BELIEVABLE FAKE BILLS.

It's tempting to think that fake bills are no longer an issue thanks to advances in security features and detection technology, but it's actually the other way around: Now, with the ability to buy inkjet printers for cheap, more people are making counterfeits than they were years ago.

All it takes to set up a counterfeiting operation is a few hundred bucks. In 2014, Bloomberg News reported on Tarshema Brice, a Richmond, Virginia-based hairstylist and janitor who produced between $10,000 and $20,000 in fake bills over the course of two years. Her scheme was simple: Brice took $5 bills and soaked them in a degreaser, then scrubbed off the ink with a toothbrush and let them dry. Next, she used a Hewlett-Packer ink jet printer to print images she'd scanned of $50 and $100 notes onto the blank bills. She was caught in 2013 and pleaded guilty to counterfeiting in May 2014.

But Brice's operation was chump change compared to Albert Talton's. According to WIRED, the Lawndale, California resident was responsible for putting more than $7 million in fake bills into circulation between 2004 and 2008. He pulled it off, in part, using ink jet and laser printers he bought at his local Staples store. He also used a variety of clever tricks: First Talton took two sheets of newspaper, which he discovered passed the counterfeit pen test, and printed imitation watermarks and security strips on the inside of one piece. Next, he glued another sheet of newspaper to the watermarked sheet. Then, he would print images of bills onto the front and back of the sheets; finally, he cut the notes of his funny money to size. Talton's bills circulated nationwide and in nine countries overseas; the counterfeiter was sentenced to more than nine years in prison in 2009.

4. FRANK BOURASSA IS THE BIGGEST MONEY COUNTERFEITER IN HISTORY.

Canadian Frank Bourassa's counterfeit money operation was no newspaper-and-ink-jet scheme: He convinced a Swiss paper company to sell him authentic rag paper, complete with security thread and a watermark, and bought printing presses and embossers to make his fake cash. He spent $300,000, made $250 million in fake U.S. money—and, in the end, got off with just six weeks in jail, even though his counterfeit money operation was the biggest orchestrated by one man (that we're aware of).

How did he get out with so little jail time? Bourassa cut a deal with Canadian authorities: He handed over $200 million in fake bills, and all he had to do was pay a fine of $1350 for drug possession—no more jail time. Canada also agreed not to extradite him, so he was safe from U.S. authorities. And he even walked away with some cash: Bourassa told GQ that he didn't disclose to the authorities that there was $50 million more of his fake cash, which he may have squirreled away—or he may have sold. "The deal was already done when they figured out that the $50 million was missing, so there was nothing they could do," he said. "So they're pissed. They're as pissed as pissed could be."

These days, Bourassa is consulting for government and business fraud protection tactics and working on a life coaching program and a memoir. "It's good," he told GQ. "I'm set. I'm home. I'm out. It's all fun."

5. COINS HAVE RIDGES IN PART TO PREVENT THEM FROM BEING COUNTERFEITED.

When the U.S. Mint was established in 1792, it produced several coins made of precious metals like gold and silver. Enterprising criminals would shave off a little part of the coin and sell the precious metal and the coin separately for a profit. Reeds (the technical name for the ridges) were added to make it obvious when a coin was “clipped,” but had a side effect of making the coin harder to counterfeit. So instead of embossing an image on both sides of the coin, counterfeiters had to add a vertical design to the coin as well.

Although modern coins aren’t made of gold and silver like they used to be, ridges are still included on coins to make it easy to distinguish between different coin denominations (largely the dime and the penny). The reeds can also be used to determine modern counterfeits of old coins. An 1873 Philadelphia dime might sell for a hundred dollars, while an 1873 dime from the short-lived Carson City mint was sold in 2012 for $1.6 million. This discrepancy has led to people buying old Philadelphia dimes and changing the mintmark to be Carson City. Thankfully, it’s easy to identify a legitimate Carson City dime: They have 89 broad reeds, while a Philadelphia dime has 113 narrow reeds.

6. COUNTERFEIT MONEY CAN BE A PROBLEM WHEN TRAVELING.

While counterfeit coins rarely make the news in the United States (though it does happen), this isn't the case in the rest of the world. The Royal Mint found in May 2015 that 2.55 percent of all 1-pound coins in the UK were counterfeit, down from 3 percent the year before. In 2004, South African businesses refused to accept the 5 rand coin because of worries of counterfeiting, which were believed to be 2 percent of all coins in circulation. Euro coins were believed to be much harder to forge than other coins, but in 2014, Italian police found over half a million counterfeit euro coins in a shipping container.

So just as you should examine money before leaving an American bank, check out the money you're handed while traveling overseas. When one New York Times writer received counterfeit cash from an airport currency exchange in Mexico, he was advised by a hotel manager against calling the police. “If you can’t prove that you got it where you say, you could be sued for slander,” the manager said. “And why get the police involved over a small sum? It’s a crime to possess counterfeit money.” The manager knew from experience: He recounted how, on a business trip to England, he'd given a cab driver a counterfeit note and ended up in jail overnight.

7. THE SECRET SERVICE WAS CREATED TO SUPPRESS COUNTERFEIT MONEY.

On April 14, 1865 (the same day he was fatally shot by John Wilkes Booth), Abraham Lincoln signed legislation that would allow for the creation of the Secret Service—not to serve as presidential bodyguards, but to help suppress money counterfeiting. Treasury Secretary Hugh McCulloch came up with the idea after Lincoln called for a commission to help stop the counterfeit money, which at that time was estimated to account for between one-third and half of the American currency in circulation. To this day, the Secret Service plays a role in creating new methods to fight against counterfeit bills, including training law enforcement operations to catch counterfeiters, investigating and apprehending criminal organizations and individuals, and raising consumer and business awareness about fake bills.