In 1992, IBM research scientists Cynthia Dwork and Moni Naor published a paper at CRYPTO 1992 titled "Pricing via Processing or Junk Mail", suggesting a possibility of using CPU-bound functions to deter abusers from sending spam. The scheme was based on the idea that computer users are much more likely to abuse a resource if the cost of abusing the resource is negligible: the underlying reason spam has become so rampant is that sending an e-mail has minuscule cost for spammers.