Security is tight with 1 million people expected on the streets of London to celebrate Prince William and Kate Middleton's Friday wedding.
Authorities are closely watching Facebook, for instance, where some activists are calling for protests along the parade route.
There is growing concern about the anger being vented online toward the royal wedding, such as a photo of William and Middleton with nooses around their necks that was posted by a group called the Anarchist Media Project.
Scotland Yard officials this morning said they are ready for anything that might disrupt the wedding.
"Any criminals attempting to disrupt it, be that in the guise of protest or otherwise, will be met by a robust, decisive, flexible and proportionate policing response," the London police officials said.
Such confidence stems from a plan described as a multi-layered "ring of steel" using 5,000 policemen -- both in uniform and undercover -- as close to the new royal couple as at the back of their carriage.
Footmen at Princess Diana's wedding 30 years ago, for instance, were actually armed undercover police. They were not just there to open the door but to take a bullet for the royal couple.
The police protection Friday will be intended to prevent violent protesters' causing chaos on the streets of London, as seen last month in a recent demonstration against budget cutbacks.
Watch a special "20/20" Thursday at 8 p.m. ET for a behind-the-scenes look at the life that awaits Kate Middleton and join us again at 4 a.m. Friday morning for ABC News' live coverage of the Royal Wedding with Diane Sawyer and Barbara Walters.
Officials Monitor Social Media
Some protesters say they are ready to walk the talk to try to disrupt the wedding, such as one Islamic group denied a permit to protest outside Westminster Abbey, in reaction to what it says were atrocities against Muslims.
Social media outlets such as Facebook and Twitter can help protesters outmaneuver the police by allowing them to mobilize quickly and efficiently.
"The Internet gives these people a huge megaphone that they otherwise wouldn't have," said Micah Sifry of the Personal Democracy Forum.
So British authorities are monitoring Facebook pages such as one by a protest group in the U.K. that calls for a "national demo" to "reclaim the royal wedding."
The last thing authorities want is a repeat of the scenePrince Charles and Camilla found themselves in when they were surrounded during a protest in December.
"If we see unusual movements of crowds or groups, we'll be tracking them, making sure no one causes any problems on the day itself," Andy Trotter of the British Transport Police said.