Several companies have been accused in court of using knowingly false announcements to gain market advantage.

Accountants generally give great weight to tax documents because the filing of a knowingly false return is a crime under Federal law.

These reports, according to the lawsuit, were knowingly false and were held while SAC accumulated its short positions.

The protection does not cover knowingly false or reckless statements.

And that means you have to show that it was knowingly false or that it was a reckless disregard for the truth.

"Should a challenger make a knowingly false challenge," the Oct. 28 letter said, "that person could be subject to criminal prosecution."

The second category is a subset of the first: knowingly false statements (deliberate lies).

Abrams defended the right of Fortune magazine to publish vicious attacks on public figures, "so long as the materials published were not knowingly false."

"We haven't found any information to indicate that testimony was knowingly false," he said.

That is largely because of the difficulty in proving that a decision based on conflicting opinions was knowingly false.