More web attacks likely, North Korea suspected

A fresh wave of cyber attacks that slowed US and South Korean websites this week could come again, a web security firm said, while the South's spy agency has said the hacking may be linked to North Korea.

The impact of the attacks, aimed at dozens of sites including the White House and the South's presidential office, was seen as negligible, experts said, but served as a reminder that Pyongyang has been planning for cyber warfare.

"The code has a schedule function," South Korean web security firm AhnLab said in a statement.

"The times and targets could change if a new strain of the computer virus is released," it said.

If the North was responsible, it would mark an escalation in tension already high from Pyongyang's nuclear test in May, a barrage of ballistic missiles in July and repeated taunts of long-time foes Seoul and Washington in its official media.

But some analysts raised doubts about the North's involvement, saying it may be the work of industrial spies or pranksters.