Former North Korean defectors and US human rights activists release balloons carrying anti-North Korea leaflets at a park in the border town of Paju, north of Seoul, on January 15, 2014 Jung Yeon-Je/AFP South Korean activists launched thousands of anti-Pyongyang leaflets and Wikipedia-loaded USB keys across the border Wednesday, despite past North Korean threats to shell the "human scum" involved.

Packages floated over the heavily-militarised border by balloon also contained 1,000 United States one dollar bills and DVDs detailing human rights abuses in the North.

"There is clearly enormous hunger for outside information in North Korea," said Thor Halvorssen, president of the US-based Human Rights Foundation, which supported the event in the border town of Paju.

"USB keys are one of the most powerful tools, because they're small, can be hidden and shared easily, and carry massive amounts of data," he said.

Each of the 1,500 USB flash drives launched on Wednesday had been loaded with the Korean-language version of the online encyclopaedia Wikipedia.

The 500,000 anti-North leaflets in the packages were also accompanied by around 50 tiny transistor radios.

While North Koreans live in what is probably the most isolated and censored society on the planet, ranking last in any media freedom survey, the country is not a complete IT desert.

Cell phones were introduced through a joint venture with the Egyptian telecom firm Orascom in 2008, the same year the state launched a domestic intranet, and some government bodies have their own websites.

And for all the regime's efforts, the information barrier erected around North Korea has, in recent years, begun to lose some of its prophylactic power.

Smuggled mobile phones from China allow people near the border to connect with Chinese servers and make international calls, while re-wired TVs and radios allow access to outside broadcasting.

Unauthorised DVDs, MP3 players and USB memory sticks have also been used to bring in everything from news reports to South Korean TV dramas.

Wednesday's balloon launch was organised by a North Korean defector group that is particularly vocal in its criticisms of Pyongyang.

"This is aimed at letting North Korean people know about (leader) Kim Jong-Un's brutality... and deliver a message to North Koreans that now is time for them to rise up and finish the dictatorship," said the group's leader Park Sang-Hak.

South Korean police have enforced bans on similar launches in the past, citing concerns from local residents about possible North Korean retaliation.