THEY are the modern scourge: cowards who use the anonymity of the internet to viciously abuse people by issuing threats to rape, mutilate or murder.

Chris Grayling, the justice secretary, better known for his tough stance on the European convention on human rights, has turned his fire on so-called trolls, people who use social networking sites such as Twitter and Facebook to harass and intimidate victims.

“People are being abused online in the most crude and degrading fashion,” Grayling said last night.

“We must send out a clear message: if you troll, you risk being behind bars for two years.”

Many of the victims of these trolls are women, among them the Labour MP Stella Creasy, the TV presenter Judy Finnigan and her daughter Chloe Madeley, and Kate McCann, the mother of missing Madeleine.

Last month McCann and her husband Gerry handed police an 80-page dossier containing hundreds of tweets, Facebook messages and posts from online forums abusing them and accusing them of being involved in the disappearance of their daughter. Some of the messages were directed at their other children, nine-year-old twins.

In September, a man who sent a string of abusive messages to Creasy was jailed.

She said: “We need to send a clear message that it isn’t for anyone to put up with being harassed via any medium — this is an old crime taking a new form online.”

The Communications Act 2003 bans online messages that threaten violence or cause stress or alarm to their targets. But the harshest sentence that magistrates can impose is six months in prison.

The government is to introduce amendments to the Criminal Justice and Courts Bill, which will be debated in the House of Lords this week, to allow a maximum penalty on conviction of two years in prison.

The period in which prosecutions can be brought against people for using the internet, social media or mobile phones to send menacing messages will be increased from six months to three years.

“The sending of abusive messages or material online can cause absolute misery for victims and we need to make sure that people who commit these awful crimes are properly punished,” Grayling said.

Creasy said that police had to ensure that victims were given proper support when they came forward. “Otherwise longer sentences will be little comfort to those still too often being told that because they are being harassed online it’s not serious,” she said.