UK - Section 127 of the Communications Act 2003
The UK Communications Act of 2003 Stipulates that it is a Criminal Offence to Send a Message on a Public Network, such as Social Media
Improper use of public electronic communications network
(1)A person is guilty of an offence if he —
(a)sends by means of a public electronic communications network a message or other matter that is grossly offensive or of an indecent, obscene or menacing character; or
(b)causes any such message or matter to be so sent.
(2)A person is guilty of an offence if, for the purpose of causing annoyance, inconvenience or needless anxiety to another, he—
(a)sends by means of a public electronic communications network, a message that he knows to be false,
(b)causes such a message to be sent; or
(c)persistently makes use of a public electronic communications network.
(3)A person guilty of an offence under this section shall be liable, on summary conviction, to imprisonment for a term not exceeding six months or to a fine not exceeding level 5 on the standard scale, or to both.
(4)Subsections (1) and (2) do not apply to anything done in the course of providing a programme service (within the meaning of the Broadcasting Act 1990 (c. 42)).
(5)An information or complaint relating to an offence under this section may be tried by a magistrates' court in England and Wales or Northern Ireland if it is laid or made —
(a)before the end of the period of 3 years beginning with the day on which the offence was committed, and
(b)before the end of the period of 6 months beginning with the day on which evidence comes to the knowledge of the prosecutor which the prosecutor considers sufficient to justify proceedings.
(6)Summary proceedings for an offence under this section may be commenced in Scotland —
(a)before the end of the period of 3 years beginning with the day on which the offence was committed, and
(b)before the end of the period of 6 months beginning with the day on which evidence comes to the knowledge of the prosecutor which the prosecutor considers sufficient to justify proceedings,and section 136(3) of the Criminal Procedure (Scotland) Act 1995 (date when proceedings deemed to be commenced) applies for the purposes of this subsection as it applies for the purposes of that section.
(7)A certificate of a prosecutor as to the date on which evidence described in subsection (5)(b) or (6)(b) came to his or her knowledge is conclusive evidence of that fact.