When the volume of spam hitting my inbox dropped suddenly last week, I thought it was just me. It seems, however, that Internet users around the world have seen a significant drop in spam. And now the intriguing story behind the sudden drop has emerged…

Brian Krebs, reporting in the Washington Post, says that at about 4:30 p.m. EST last Tuesday, the volume of spam being delivered across the world dropped by about 65 percent. It seems that various Internet service providers discovered that a web hosting company in Silicon Valley called McColo Corp. was hosting organizations responsible for much of the world’s spam.

Unfortunately, the relief is likely to be temporary. Those spammers are likely to find other hosts! But Brian Krebs asks a reasonable question: why did it take so long for anyone to work out that a firm in the heart of the Internet and computing community - we’re talking Silicon Valley of all places - was distributing the bulk of the world’s spam?

It appears that McColo - which has not been charged with any crime - hosted a number of key Internet servers (i.e. computers that host websites and send out email, etc) which controlled networks of computers. These networks were used by their various owners to turn hundreds of thousands of compromised PCs into spam distributors or ‘botnets’.

McColo effectively ran the ‘master servers’ that the various dodgy spam organizations used to take over the botnets which, in turn, were used to send out all the spam. When McColo’s Internet service providers took it offline, the master servers went offline… which meant the botnets could no longer be used to send out spam.

Source: Brian Krebs, “Answers Trickle Out as Spammer Networks Remain Compromised”, November 19, 2008