Hundreds of thousands of athletes and tourists are about to arrive in Rio de Janeiro from around the world for this year's Summer Olympics, whose opening ceremony is just more than two weeks away. Security is going to be extremely tight. The police and army are on high alert for copy-cat attacks after European cities have suffered one terrorist assault after the other.

A vast ocean separates Brazil from the violence that has engulfed Syria and Iraq, but networks of terrorists spread messages through encrypted channels these days. On Monday, an obscure Brazilian outfit called Ansar al-Khilafah pledged allegiance to the Islamic State on a Telegram channel, according to the SITE Intelligence Group.

Telegram is a messaging app that, like Whatsapp or Viber, allows users to send encrypted messages. Telegram also hosts private channels. That combination has made the app a haven for terrorist groups looking to recruit, coordinate and simply brag to each other.

SITE also indicated that Islamic State channels on Telegram had been translated into Spanish and Portuguese. This would be the first time any organized group in South America has taken such overt steps to affiliate itself with the militant group.

Before the attack in Nice, France, last week, Rio de Janeiro had already planned to deploy 85,000 police, military and members of a Brazil-style national guard called the National Force. But Brazil increased its plans in response to the Nice assault. The country's defense minister told reporters at Rio's airport that Brazil had a database of 500,000 people suspected of some association with terrorism, compiled with the help of the United States and France.

“Anyone wanting to watch the Olympic Games will have to go through a barrier where they identify themselves and their details are checked,” he said. “This person will then pass through a second barrier where everything they are bringing with them will be scanned.”

Brazilian security forces have been engaged in mock-attack drills this week near stadiums and on public transportation.

In November, after the coordinated Paris attacks claimed by the Islamic State, a French extremist posted on Twitter that Brazil was the "next target," causing some to think twice about attending the Games. The chatter on Telegram has increased those jitters.

"The opening of this new front in the spreading of information for extremist indoctrination, aimed at the Portuguese-speaking public, increases the complexity of the job of tackling terrorism," Brazil's intelligence agency said in a statement.

The presence of Ansar al-Khilafah on messaging apps could increase the likelihood of a lone wolf becoming radicalized. Guns are easily obtainable in Brazil, both in crime-ridden slums and across the porous border with Paraguay, where an extensive small-arms trade takes place.

Read More: