I'm pretty sure that in the US, it not only has to be false, but the person making the statement must have either known it to be false, or shown negligence in not verifying the veracity of the statement.
Libel lawsuits in England are similar to patent lawsuits in Texas - you know that the venue was chosen mainly because the person filing the suit wanted the friendliest court possible.
The freedom of speech devices in the Constitution prohibit anonymity, rendering themselves ineffective.