In 1997, Vipul Ved Prakash dropped out of Delhi University “for want of undisturbed coding time,” as he puts it. He then cofounded Sense/Net, one of India’s first privately owned Internet service providers, but soon encountered the scourge of spam. Customers paying by the minute for their connections complained they were wasting time deleting inwanted e-mail. So Prakash developed Vipul’s Razoe, a spam-fighting, opensource software tool available online for free. Thousands of users downloaded the “collaborative filter” program, which allowed them to keep messages or move them into spam folders. Vipul’s Razor transmitted those decisions to a central server, and if a majority of users discarded a given message, it would therefore be blocked for the entire group. After moving from New Delhi to California in 2000, Prakash worked for a time at Napster and then cofounded Cloudmark with Jordan Ritter, Napster’s former software chief. The San Francisco startup adapted Vipul’s Razor into a tool called SpamNet that today boasts 500,000 users. Initially free, it now costs $3.99 per month. “When a new person joins,” Prakash says, “they get the benefit of the entire community.” Cloudmark also markets Authority, a corporate version of SpamNet.