AVERAGE internet speeds fell sharply in Australia during 2012, according to a new report that ranked the country 41 out of 98 nations for the pace of its online connections.

Average connection speeds fell 23 per cent in the calendar year 2012, against a global rise of five per cent, according to the latest State of the Internet report by Akamai Technologies, a US-based computing firm.

The average connection speed in Australia by the end of 2012 was said to be 4.2 megabits per second - placing it 28th among the 34 Organisation for Economic Co-operation and Development (OECD) nations.

That is less than a third of the speed in South Korea, which despite recording a 13 per cent decline, still had the fastest average internet connections in the world with 14 megabits per second.

The global average was 2.9 megabits per second.

"Australia's decline is unexpectedly high, especially given the progress being made on the national broadband network (NBN)," the report said.

It did not offer a clear reason for the decline, but said it was "out of character" and likely to be improved.

"These negative trends are of concern, but high broadband adoption in South Korea remains strong, and the decline in Australia is out of character," it added.

"Furthermore, ongoing NBN deployment in Australia should help to turn the trend positive again going forward."

Under Labor's NBN plan, consumers would experience speeds of 100 megabits per second by 2021, with the infrastructure roll-out costing $37.4 billion.

The Coalition's plan would cost $20.4 billion and be completed by 2019, but with slower minimum download speeds of 25 megabits per second.

The Akamai report fingered China as the world's major source of cyber attacks.

"China once again overwhelmingly remained the source of the largest volume of attack traffic, accounting for two-fifths of the total, up from a third in the prior quarter," it said.

The US was the next highest source of cyber attacks, followed by Turkey, Russia and Taiwan.

The report data suggests the US still has the most internet subscribers, followed by China, Japan, Germany and the UK.

Overall there was a 9.8 per cent rise in internet subscribers during 2012.