Libel includes information that is false, defamatory, and a matter of fact rather than opinion. The author must act negligently against a private figure, or with injurious intent against a public official.

In Massachusetts, a written or oral statement defames if it discredits or "holds up to scorn, hatred, ridicule or contempt in the minds of any considerable and respectable class of the community," according to the Massachusetts Bar Association.

Judges have distinguished blog posts from comments online, said Peter Scheer, executive director of the First Amendment Coalition, a nonprofit that works to advance free speech. A blogger is legally responsible for his or her posts, not what others write, he said.

Lowell Sun: You libel, you're liable