A group known as Anonymous Philippines advertised what was billed as a "Million Mask March," scheduled for Tuesday at the country's House of Representatives in Quezon City near Manila, The Philippine Daily Inquirer reported Sunday.
The hackers posted the group's name in the Office of the Ombudsman's website.
Clicking on the name redirects visitors to an Anonymous Philippines logo and a letter, the newspaper said.
"We apologize for this inconvenience, but this is the only easiest way we could convey our message to you, our dear brothers and sisters who are tired of this cruelty and this false democracy, tired of this government and the politicians who only think about themselves," the letter said.
The letter said the rally was to be a "peaceful march to meet and greet like-minded individuals."
Exploding whale video goes viral on Internet
Martin Bashir resigns from MSNBC over Sarah Palin comments