"Russians feel safer when they take public transport." That's one of the findings the country's state-owned VTSIOM polling institute published in late August. It suggested that two-thirds of the people polled said they were happy with the security measures in buses, trains and other forms of public transport. The fear of terror attacks had "declined noticeably" over the past two years, according to the study.

A black widow from the Caucasus

But now fears of Islamist terror have returned to Russia after an explosion in a public bus in the city in the southern city of Volgograd killed at least six people. A suicide bomber appears to have been responsible for the blast. Some of the victims are still in critical condition, so the number of victims could still rise.

The bomber is believed to have been a so-called "black widow," female suicide bombers who are often wives or partners of Islamist militants. In this case it's thought to have been a 30-year old woman from Makhachkala, capital of the country's Dagestan province in the North Caucasus.

Stepping up security

The fact that Russians recently began to feel safer might have to do with the country's heightened security measures. Buses, trains and billboards warn citizens to be on the alert for potential terrorist attacks.

Since July, Russia has been collecting data on people traveling by air, road and rail, and making this available to the country's domestic intelligence agency, the FSB. A draft bill would also allow security personnel more leeway in using their weapons.

Dagestan the most dangerous province

Since the war in Chechnya began in 1994, Russia has seen several major terror attacks by insurgents, including the hostage-taking at a Moscow theater in 2002 and the Beslan school attack in 2004, which were both perpetrated largely by Chechen Islamists. And while Moscow long ago declared the war in Chechnya to be over, militant groups have continued their war underground.

Yet it is Dagestan, not Chechnya, that has become the country's most dangerous province. Some 60 percent of the 316 terror attacks the national anti-terror committee has logged since 2012 took place in Dagestan. This year is expected to be no different. On an almost daily basis, bombs go off in the province, often targeting police or members of the judiciary. In late September 2013, the region's highest judge and his son were shot dead in their car.

Prevention

Moscow and other large Russian cities have been largely spared. But in January 2011, a bomb went off at the capital's Domodedovo airport, killing 37 people. Authorities traced the attack to the North Caucasus.

Some experts, like Alexey Mukhin, director general of the Center for Political Information, believe that this "pause" is linked to the situation in North Africa and the Middle East. International Islamic terror organizations had shifted their focus to those regions, Mukhin told DW. But Russia's strong support for the Syrian government caused anger among the Islamists fighting President Bashar al-Assad. Mukhin said it was therefore quite possible that there was a link between Moscow's position on Syria and the blast in Volgograd.

Mukhin also pointed to the success of prevention efforts undertaken by Russian intelligence. Several attacks have been averted. On October 15, two men were arrested who had allegedly been planning an attack on a chemical plant. In May 2013, police took out a terror network in a small town east of Moscow, Orekhovo-Zuyevo, who they said had been planning an attack in Moscow. Some of the suspects in the case had trained in terror camps in Afghanistan and Pakistan.

Concerns ahead of Sochi

The explosion in Volgograd is raising concerns ahead of the Winter Olympics in Sochi in February 2014. "The reasons for the attack are linked to the upcoming Olympics in Sochi," Alexei Filatov, vice president of the veterans of the Russian anti-terror unit Alfa, wrote in his blog. The point was to test Russia's strength, he suggested.

The city is not far from the North Caucasus and for years there have been warnings that terrorists might be planning a major attack at the event.