"She said that Cloudmark is currently revising that 8 per cent estimate upwards.Because of its huge base -- last month Facebook said it had more than 300 million users -- the site is a frequent target for hackers and identity thieves.Last March, for example, the Koobface worm made the rounds on Facebook, as well as other social networking sites such as MySpace and Friendster, infecting large number" . . . . .