The volume of spam email being sent across the internet plummeted yesterday, after a San Jose-based company was taken offline.

McColo, a web hosting company based in California, was believed to be responsible for up to 75 per cent of the spam sent in the United States. It hosted websites for foreign companies who were engaged in the online sales of a variety of products, including counterfeit pharmaceuticals and child pornography, according to the Washington Post, whose 'Security Fix' blog reported suspicious activity to McColo's service providers.

Spam is commonly sent using networks of hacked computers known as 'botnets', who transmit the messages without the knowledge of the computer's owner. Home computers are often used to solicit responses from unwitting internet users. It is believed that many of the most prolific of these botnets were hosted by McColo.