isoloisti writes: In surveys men claim to have had more female sex partners than women claim male partners, which is impossible. The reason? A few self-described Don Juans who tell whoppers pull the average way up, and errors don't cancel. Cyber-crime estimates are hopelessly exaggerated for exactly the same reason according to a new study to appear at the Workshop on the Economics of Information Security. The authors write: “‘You should never trust user input’ says one standard text on writing secure code. It is ironic then that our cyber-crime survey estimates rely almost exclusively on unverified user input. A practice that is regarded as unacceptable in writing code is ubiquitous in forming the estimates that drive policy." In many cases 75% of the estimate comes from the unverified self-reported answers of one or two people.