The attorney general of California has opened an investigation into ACORN and the circumstances under which its employees were secretly videotaped, California Gov. Arnold Schwarzenegger announced on his Twitter page Thursday.

Schwarzenegger wrote he had "just heard" that the state's attorney general, Edmund G. Brown Jr., is opening an investigation following the release of five hidden-camera videos that depicted ACORN employees offering advice to filmmakers James O'Keefe and Hannah Giles, who posed as a pimp and prostitute, on how to skirt tax laws and avoid detection by authorities.

"Just heard from Atty Gen Jerry Brown that he is opening an investigation of ACORN in Calif," the governor wrote.

But according to a Sept. 25 letter from James Humes, California's chief deputy attorney general, an investigation had been launched last week.

"The Attorney General shares your concerns and he takes seriously his obligation to see that the laws of California are uniformly and adequately enforced," the letter read. "Accordingly, we have opened an investigation of both ACORN and the circumstances under which ACORN employees were videotaped."

The footage -- captured in ACORN offices in Baltimore, Washington, D.C., Brooklyn, San Diego and San Bernadino, Calif. -- has led to the firing of four employees, the suspension of two others and prompted the IRS and the Census Bureau to sever all ties to the organization while Congress voted to cut federal funding.

The videos, which were first posted on BigGovernment.com, have also prompted a review by the Treasury Department's inspector general and a criminal probe by the Kings County District Attorney's Office to investigate activities at the Brooklyn office.

Scott Gerber, a spokesman for Brown, confirmed that a probe into ACORN and the videotaping of its employees has been launched.

"We're going to follow the facts without fear or favor," Gerber said.

New York State Attorney General Andrew Cuomo launched a probe into grants given to ACORN by state lawmakers on Sept. 15.

A day later, on Sept. 16, Bertha Lewis, ACORN's chief organizer, announced that the organization would stop taking "new intakes" immediately, essentially freezing its service programs. Scott Harshbarger, a Boston attorney and former attorney general of Massachusetts, was hired last week to conduct an "independent and comprehensive" investigation into the liberal activist group.

ACORN has also filed a lawsuit against O'Keefe, Giles and Breitbart.com, a Web site managed by conservative commentator Andrew Breitbart, which posted the videos.

The lawsuit, filed in a Baltimore court, stems from an undercover video showing ACORN employees Shera Williams and Tonja Thompson providing advice to two filmmakers posing as a pimp and prostitute on how to skirt tax laws.