An arm of the FBI that watches for cybercrime and online security threats today warned that Chinese hackers may escalate their attacks on US Web sites and mail servers early next month.

The National Infrastructure Protection Center (NIPC) said recent events between the US and China, such as the military aircraft collision that left a Chinese flier dead, already triggered Web page defacements. "To date, hackers already have unlawfully defaced a number of US Web sites, replacing existing content with pro-Chinese or anti-U.S. rhetoric," the NIPC said in an advisory posted on its Web site. Some of the messages sent to the US from angry Internet users in China encourage revenge for the death of Chinese pilot Wang Wei, who died when his military jet crashed into a US spy plane. One posting from China said, "Hack the USA!!! For our pilote (sic) Wang!!! For our China!!!" the Washington Post reported earlier this month. Additionally, US authorities say an Internet worm named "Lion" with a China connection has been unleashed, and is infecting computer systems with tools to touch off distributed denial of service (DDOS) attacks. The NIPC said the stepped-up activity may be designed to coincide with dates remembered in China - May 1 is May Day; May 4 is Youth Day; and, May 7 is the two-year anniversary of the accidental bombing of the Chinese Embassy in Belgrade. "Chinese hackers have publicly discussed increasing their activity during this period, which coincides with dates of historic significance in the PRC (People's Republic of China)," the NIPC advisory said. The National Infrastructure Protection Center is on the Web at http://www.nipc.gov