Citizens of the Marshall Islands in the South Pacific have been left without a functioning email systems following a denial of service attack on the country's sole ISP.

It could take days to full restore service, the general manager of the Marshall Islands National Telecommunications Authority (NTA) told Radio New Zealand International. Systems at the monopoly carrier were taken offline by a flood of email traffic from compromised PCs.

NTA systems were hit by a sudden four-fold increase in incoming traffic as a result of the attack. Mail gateways wilted under the assault of more than 500 SMTP connections per second, according to local reports.

"These unusually high numbers of connections did not actually deliver email messages as the mail queues on our incoming mail gateways remained empty. This is quite different from the normal spam attacks we see daily; spam actually tries to flood our queues with email messages, however, this attack was designed to keep our servers constantly locked to zombies, while blocking legitimate email," Tony Muller, NTA’s general manager, explained.

The motives for the assault are unclear. NTA customers are only able to exchange email messages with each other and not the wider world as a result of the junk mail onslaught, which began early on Tuesday. ®

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