A group of Internet service providers this week is launching the so-called "six strikes" program, aimed at curbing piracy on peer-to-peer networks. The new "Copyright Alert System" calls for ISPs to penalize suspected infringers with a series of escalating sanctions. Participating ISPs, including AT&T, Cablevision, Comcast, Time Warner and Verizon, intend to start off by sending warning letters. Users who ignore them -- or who are suspected of doing so -- could then have to visit education sites. Eventually ISPs could throttle some of those users, though some have said they have no intention of doing so.