To watch out for other fakes, people should look carefully for obvious signs like misspellings and typographical errors, incorrectly colored packaging or computer type fonts slightly different from familiar brand logos. They should be aware that increasingly, companies are attempting to protect their copyrights with security features similar to those on currency, experts say, so they should look for those if they know they exist elsewhere.
And people should be especially mindful of where they buy products. "If you buy the product on the street or a flea market … you should not be surprised if the product is a fake," Lowe said.
For various reasons, even legitimate stores might occasionally sell fakes, Lowe said, as product counterfeiters — increasingly connected to organized crime and terrorism because of "high profit" and "low risk," he believes — try "to get products into legitimate supply chains."
One method involves so-called parallel-traded goods, experts say. Authentic goods can be sold in different parts of the world for different prices. Opportunists might divert goods from less-pricy markets back into expensive ones like the United States and Europe, assuring merchants that they are diverted, but authentically made, goods.
But, at some point, Lowe said, they could start slipping in counterfeit items.
"Some can be quite deceptive," Hopkins said. "If [alleged Microsoft software] you're buying is packaged in something that looks authentic, shrink-wrapped … you don't know for sure whether that's authentic software or not."
Even experts can have a tough time telling the real from the fake.
"Some manufacturers have said to me that we can't really tell the fake from the genuine unless we really take them to bits and examine the pieces," Lowe said.
"There's a recent case in the U.K. where Johnnie Walker Black Label whisky was counterfeited," he added, describing meticulously copied boxes, labels and bottles. "It actually contained methanol, which is a harmful substance. The fake was actually a fairly convincing one. … You could only really tell the slight differences when you had the genuine and the fake articles side by side."
Such attention to detail is not always standard with currency counterfeiters.
Like the U.S. Bureau of Engraving and Printing, U.S. currency counterfeiters traditionally have plied their trade using offset printing equipment. But the percentage of counterfeits done with digital, computer-aided equipment is believed to have risen from about 1 percent of fake bills in 1995 to 40 percent in 2002, according to federal estimates.
Generally, officials say, the offset-printed fakes are more convincing, with a better chance of approximating genuine bills' security features — which include colorshifting ink, watermarks and embedded security threads.
A redesigned $20 bill to be circulated later this year will have even more safeguards, including improved "optically variable ink," which changes color when viewed from different angles, variable tints to paper stock, and more printed color and graphics. The features are highlighted at http://www.moneyfactory.com/newmoney/.
But there's a factor that can make all the security measures in authentic currency irrelevant: A gullible public.