I recently read a fascinating account of some little-known history, Stephen Mihm's "A Nation of Counterfeiters: Capitalists, Con Men, and the Making of the United States" (Harvard University Press, 2007, paperback 2009.) Before the Civil War, paper money was issued and circulated on behalf of numerous banks, whose quality varied from sound to weak to wholly fictional. Absent national uniformity and rapid communications, it was very hard to determine whether a particular bill was legitimate or valid, opening up opportunities for many fraudulent activities, whether copying, modifying, or fabricating currency. (The Cogniac Street of this post's title, e.g., refers to a road across the Canadian border, in a then-remote area of Quebec, on which most inhabitants were alleged to be involved with counterfeiting enterprises.) In an environment where banks often failed, there wasn't uniform consensus that banks' notes should be respected and accepted, or that a counterfeiter's creation of money was necessarily less valid than a bank officer's action in doing so.
In response to the chaotic situation, a number of subscription "detector" services developed, providing information to be used to detect false bills in reaction to observed counterfeits. There's an analogy to the lists that were once printed and distributed (are they still?) to list invalid credit card numbers, but many of the detector criteria were more subtle or ambiguous than the presence or absence of a number on a list. Further, the detectors' quality was itself compromised by conflicts of interest; for example, publishers were sometimes engaged in brokering the redemption of notes from distant banks, so could benefit by lowering the ratings of sound bills in order to obtain them at discounts. In any case, the detector business depended on continuing uncertainty as to whether a new and unfamiliar bill should be trusted, and sought to reassure its subscribers with periodic updates providing a form of independent validation. In a sense, it acted as an anti-malware service in the context of early 19th century financial networks.
PS: I see now that Mihm's book is currently #586,833 on the Amazon.com Bestsellers Rank list. Long live the Long Tail!