A virulent computer worm that hobbled the global Internet today affected stock trading in South Korea.
South Korea, the world's most wired country, was hit hardest by the "SQL Slammer" worm, which forced firms worldwide to clean up computer systems after the virus spread through network connections, shutting Web servers at the weekend and slowing the Internet.
Financial markets in Korea saw steep falls in shares of Internet service providers and gains for web security firms, although the impact of the attack, which started early on Saturday, could have been far more serious on a working day.
Shares in South Korea's two largest Internet service providers, KT Corp and Hanaro Telecom Inc, fell sharply, and web security firms Ahnlab and Hauri jumped by the daily limit high of 12 per cent.
The virus hit South Korea particularly hard because it has the world's highest penetration of broadband Internet services, which are up to 100 times faster than dial-up modem services.
Only 40 per cent of South Korean firms have installed firewalls to protect their computers and servers from electronic attacks, web security firms said.
Some Web servers in India and China were also badly affected.