Web infrastructure technology provider Akamai is co-operating with US law enforcement agencies after it was hit with a distributed denial of service attack that slowed some of its customers' sites for over two hours.

The attack utilised thousands of 'zombie' PCs, which had been infected with malicious software and used without their owner's knowledge.

Affected customers included Microsoft, Apple and Yahoo, according to web hosting market watcher Netcraft.

In a statement, Akamai apologised for the impact the attack had on customers and said it would take steps to protect them and itself against the effects of future attacks.

The company explained that the attack hit its domain name service (DNS) and "resulted in delays in DNS name resolutions and, in some cases, timed-out DNS requests".

Akamai added that some internet end users trying to reach affected sites experienced slow responses from its DNS servers, resulting in page time-outs.

The company claimed that the DNS impact was limited to only four per cent of its customer base, but that two per cent had been noticeably affected.

And less than one per cent of its customers had a significant impact affecting more than 20 per cent of their users.

Graham Titterington, senior analyst at Ovum, said: "Akamai has an enormous, well-connected network so on one level the attack could be construed as showing that no-one is invulnerable.

"This is a case of people demonstrating their power and capability, either for kudos or possibly to offer their services to others."