Early on Sunday, the hackers defaced the official Web site on pages reserved for Secretary-General Ban Ki-moon with slogans accusing the United States and Israel of killing children.

The United Nations quickly removed the hackers' messages and on Monday stopped updating the site while the system was assessed, U.N. spokeswoman Michele Montas said.

In addition to the main U.N. site, the web pages for the Economic and Social Council and the Paris Web site of the U.N. Environment Program were also attacked, Montas said.

She said U.N. investigations were underway and "quick action was taken to prevent damage to the computer system." Key financial information was not affected, she said.

A repeating message on the secretary-general's page read: "Hacked By kerem125 M0sted and Gsy That is CyberProtest Hey Ysrail and Usa, Dont kill children and other people Peace for ever No war" according to snapshots of the site by bloggers.

One of the three hackers claimed to be Turkish.

CNET, a computer and technology publisher. "The perpetrators appeared to have used a well-known and highly preventable technique called SQL injection, which takes advantage of flawed database programming to activate malicious lines of code," CNET said on its web site.

The defacements, which affected the secretary-general's site and news pages (HTTP://www.UN.org/news) were cleaned within hours, Montas said.

In an e-mail to CNET's news.com Web site, Giorgio Maone, an Italian software developer who has worked with the world body, said, ¡°The U.N. staff just deployed a cosmetic patch, which hides it from the most obvious tests, but it cannot prevent an attack¡± and said he had offered his assistance.

At the Web site www.M0sted.org, there is a list of sites allegedly hacked by the group, including Harvard and other universities and Norfolk and Norwich University Hospital in Britain, CNET said.