An online assault on a California company knocked out some of Vodafone's internet services yesterday.
Hurricane Electric, which provides Vodafone's international internet services, was struck by a denial of service attack around 11am.
Such an attack involves an organised group of web users all accessing a computer server at the same time.
This disrupts services and usually causes the server to buckle under the extra traffic.
When Hurricane Electric went down, Vodafone users were unable to gain access to some websites in the United States.
Vodafone communication spokesman Matt East said residential, business and mobile internet customers were affected.
"People who were browsing locally probably wouldn't have noticed," he said.
"But it could have hit all of our customers if they had been browsing internationally.
"Websites such as the Washington Post ... you just couldn't get to them, they were just cut off."
Customers were unable to access social networking website Twitter, but East said he did not know if Facebook was affected.
Services were restored around 2pm.
East said other internet companies could have been affected by the loss outage, however neither Telecom nor Orcon reported problems.
Denial of service attacks are proving increasingly popular with hackers looking to disrupt online services.
In March, the "hackivist" group Anonymous threatened to hit the Internal Affairs website with a denial of service attack over its plans to introduce internet filtering.
Other targets of denial of service assaults this year have included the CIA and businesses such as MasterCard and Visa.
Whistleblower website WikiLeaks was struck by a denial of service attack last November when it was releasing classified US State Department documents.