The attackers are throwing so much digital traffic at online networks that they have reportedly disrupted access to popular sites such as Netflix, the on-demand TV streaming service.
Tonight there were fears that any worsening of the attack could affect web browsing and emails.
The onslaught has focused attention on the extent to which modern communications depend on the internet. Matthew Prince, chief executive of CloudFlare, one of the firms dealing with the assault, likened it to a series of digital “nuclear bombs”. “It’s so easy to cause so much damage,” he added.
The attack is believed to have begun last week, when Spamhaus, an anti-spam organisation, was hit by a wave of digital traffic that knocked its website offline.
The body draws up lists of the servers used to send spam messages around the world. Email administrators use these lists to block spam.
But last week one of the spammers irked by Spamhouse’s work is believed to have launched the massive distributed denial of service, or DDoS, attack to bring down the anti-spam group.