A huge (wo)manhunt is under way in Russia as authorities seek four so-called “black widows” believed to be plotting terrorist attacks to disrupt the 2014 Winter Olympics in Sochi.

In and around Sochi, fliers have been posted alerting the public about “black widow” terror suspects Zaira Allieva, Dzannet Tshakhaeva, Oksana Aslanova and Ruzanna Ibragimova. On Monday, Russian security officials said they had reason to believe that Ibramigova, 22, penetrated the 1,500-mile “ring of steel” security encompassing Sochi and surrounding areas. Police were less clear about the whereabouts of the others, only saying that the suspects “are probably among us.”

Authorities are concerned that the black widows may be planning suicide bomb attacks in Sochi or near the Olympic host city. The suspects are known as “black widows” because their husbands were killed by Russian forces in the volatile Caucasus region and they may be seeking to avenge their deaths. Three of the black widows hail from Dagestan while Aslanova, 26, is from Turkmenistan. The posters warn that the women may be hiding in plain sight by substituting Western clothing for their traditional Islamic garb.

NBC News terrorism analyst Evan Kohlmann said the fact that police have put up posters of the black widows suggests “gaping holes in security right now in Sochi.”

Christopher Swift, a Georgetown University professor who has studied extremist groups in the area, concurred, telling ABC News that the developments show that security around the Olympics is not as airtight as Russia wants the world to believe. “The fact that one individual either was able to stay in the area before the ring of steel went up or get through it really raises questions about the strength of the Russian security apparatus,” he said.

Russia expert Andrew Weiss told the network that the small-scale terror operations that are being feared are difficult for counter-terrorism forces to thwart.

“The added part of this is the regional, small-cell-based structure,” Weiss said. “It’s very hard for forces to penetrate that. That’s been a chronic problem for the Russians all along.”

In addition to the black widows, authorities are seeking two men – 21-year-old Ruslan Saufutdinov and 25-year-old Murad Musaev – who may be planning attacks in southern Russia.

Police believe Ibramigova, who walks with a limp and has a 10-centimeter scar on her left cheek, entered the Sochi area around 10 days ago. Her husband was killed by Russian forces last month.