A 17-year-old Australian schoolboy today said he unwittingly caused a massive hacker attack on Twitter which sent users to Japanese porn sites and took out the White House press secretary's feed.

Pearce Delphin, whose Twitter name is @zzap, admitted exposing a security flaw which was then pounced upon by hackers, affecting thousands of users and causing havoc on the microblogging site for about five hours.

Delphin, who lives with his parents in Melbourne, said he tweeted a piece of "mouseover" JavaScript code which brings up a pop-up window when the user hovers their cursor over the message.

But the idea was soon taken up by hackers who tweaked the code to re-direct users to pornographic sites and create "worm" tweets that replicated every time they were read.

"I did it merely to see if it could be done... that JavaScript really could be executed within a tweet," Delphin told AFP via email.

"At the time of posting the tweet, I had no idea it was going to take off how it did. I just hadn't even considered it."

Twitter apologised to its millions of users after the "mouseover bug" raged through the site, opening pop-up windows in Web browsers and automatically generating tweets from other accounts.

White House press secretary Robert Gibbs and Sarah Brown, wife of Britain's former prime minister Gordon Brown, were among those hit by the bug before engineers patched it up.

The "Netcraft" security website traced the malicious code back to Delphin, who said he got the idea from another user who employed a similar code to make his profile and tweets rainbow-coloured.

"After that, it seems like some of my followers realised the power of this vulnerability, and within a matter of minutes scripts had taken over my timeline," Delphin said.

"Hopefully I won't get in trouble!" he added.