It's become a familiar pattern: after the tragedy, the spam.

The U.S. Federal Bureau of Investigation is warning computer users to be wary of unsolicited e-mail messages trying to raise money to help victims of last week's massive earthquake in China's Sichuan province.

The scam e-mails offer free vacation trips to the largest donors and may use fake logos of real online payment services in order to trick their victims, the FBI said. Similar scams followed tragedies such as Hurricane Katrina, the Virginia Tech shootings and the Sept. 11 terror attacks on the U.S., the FBI said in an advisory, dated Tuesday.

The 7.9-magnitude earthquake struck May 12, with its epicenter about 45 miles (72 kilometers) west of Chengdu. More than 41,000 people are confirmed dead after the disaster, and hundreds of thousands more have been injured.

Scammers are sending phony e-mails, some of them extremely long and filled with personal anecdotes, using titles such as "Help me," "Help me please. Read through the letter" and "Last hope. Help me please," according to Sam Masiello, director of threat management with security vendor MX Logic. He has blogged about the scams here.

The e-mailers try to start a correspondence with the victim and then try to arrange a money transfer, he said. "This is one of your classic 419-type scams," he said in an interview.

MX Logic is intercepting several thousands of these scam e-mails each hour and has also seen some messages that contain malicious Word attachments, which are used to install unauthorized software on the victim's computer.

Criminals have also reportedly hacked into the Red Cross' China relief Web site and opened fraudulent bank accounts to siphon off relief funding.

"With every tragedy that's out there, it happens," Masiello said. "The human side of me hopes that they won't, but the security side of me knows that they will."