Mariupol resident Viktoria Levashina was hoping to have a relatively easy time passing through the Kremlin-imposed process for weeding out "undesirable" Ukrainians living in territories now controlled by Russia.
A 60-year-old accountant at a construction firm, Levashina's occupation and demographic profile would not have raised red flags.
When her turn came late one night in April for her in-person background check at a so-called filtration center outside the Azov Sea port city, Levashina handed over her passport and mobile phone to the authorities and waited for a pass to travel on to Russia.
It did not come.
Levashina knew the authorities combed through phones looking for compromising information, so she handed over a gadget belonging to her recently deceased 84-year-old mother instead. Unlike her own, it was nearly empty of data and contacts.
What Levashina did not know was that the authorities would also independently search her social-media profiles on their own computers and phones. They did not like what they found and called her into a tent for interrogation.
"A dill, a Banderite," Levashina recalled an official yelling at her. "Dill" is a racist term for Ukrainians, while "Banderite" is a synonym for "Ukrainian fascist."
"I'm going to cut you to pieces!" he said in anger.
The official was incensed that she had added a Ukrainian flag to her Facebook avatar, she said.
The official informed her she was banned from traveling to Russia for 10 years, gave her a slight kick in the backside, and told her to "f*ck off" to Lviv, the western Ukrainian city noted for its patriotism, she said.
He handed back her passport and telephone, escorted her out of the tent, and left her in the darkness alone.
"I am doomed," Levashina said in a text message to her cousin Sasha in Israel and seen by RFE/RL.
WATCH: Ukrainian Woman Recounts 'Shocking' Treatment At Russian Filtration Camp
Having lost her home in the war and with no safe way of getting to Ukrainian-controlled territory, Levashina had been hoping to make her way to her relatives in Israel via Moscow.
Levashina's harrowing experience at the filtration center is not unique. She is one of hundreds of Ukrainians who have recalled invasive, abusive, and sometimes violent experiences at the many centers set up in Russian-occupied Ukrainian territories.
While some Ukrainian citizens in the occupied territories voluntarily come to the filtration centers to receive a pass to enter Russia -- where they may have close family or friends -- or to move freely around the region, others are forcibly taken there.
Regardless of how Ukrainian citizens arrived, they are all treated like criminal suspects: They are fingerprinted, photographed, and their identification documents are scanned. They are registered in a database that includes their occupation, family members, and address.
The data could be invaluable as the Kremlin moves forward with plans to hold so-called referendums in the occupied regions on joining Russia, experts said -- polls that could serve as a pretext for annexation as happened in Crimea in 2014.
The contents of their phones are examined for any signs of communication with members of the Ukrainian military or territorial defense units, or anti-Russian comments. The authorities download their phone data, including contacts.
Many are also strip-searched for signs of combat experience or pro-Ukrainian tattoos that the Russian authorities deem "fascist" and are questioned regarding their attitudes about the war.
Those raising suspicion are interrogated further and sometimes beaten. Some have not been seen again.
Ukrainians that don't pass the filtration process, especially men with combat experience, may end up in prison, their exact whereabouts and status -- alive or dead -- unknown.
Others that tend not to pass the filtration process include local government officials, activists, and people who have expressed patriotic sentiments.
Oleksandr, a student from Mariupol, said he was detained along with a friend by pro-Moscow separatists in early March, about two weeks after Russian President Vladimir Putin launched his invasion of Ukraine.
The two were taken to a small filtration center, possibly one for Ukrainians suspected of military ties, where they were beaten for anti-Russian comments they had made in an online chat, interrogated, strip-searched, and placed in a cell with just one mattress.
Oleksandr and his friend were then moved to a larger filtration center for the general public, where they were registered in a database and again searched and questioned before being given permission to travel to Russia, where they were eventually reunited with their families.
Ukrainian and Western officials, as well as human rights organizations, have said Russia's filtration centers violate the Geneva Conventions, which established international standards for conduct during conflict.
In a statement last month, the U.S. State Department called the filtration camps a war crime -- one of many Russian forces have been accused of since the invasion began -- and demanded the Kremlin dismantle them.
The number of filtration camps has grown as the war has dragged out, from a handful at the outset to around 18 now, according to estimates by the Ukrainian rights group Euromaidan SOS and U.S. officials.
As many as 1.6 million Ukrainians may have been detained, interrogated, and registered at filtration camps, according to Euromaidan SOS.
Current Time has identified at least nine filtration centers.
They are buttressed by dozens of checkpoints manned by Russian troops or separatists throughout the occupied territories.
Ukrainian citizens have no rights in Russia or in the occupied territories without a filtration pass, said Stanislav Miroshnichenko, a journalist and a member of the Media Initiative for Human Rights, a Kyiv-based organization.
The threat of being interrogated at checkpoints will prompt some to go through the filtration process themselves.
However, "sooner or later, the militants will come to every local resident," Miroshnichenko said.
John Herbst, who served as U.S. ambassador to Kyiv from 2003 to 2006, said the filtration process could be a powerful tool in the hands of the Kremlin as it seeks to impose its will on Ukraine.
"Moscow still has the subjection of Ukraine as an aim, and to do that they want to understand the human terrain," he told RFE/RL. "They want to know who are their friends and who are their foes."
Russia will mine data, including who is potentially a patriot and sympathizer, in an attempt to map out Ukrainian society, he said.
That data could come in handy as Moscow-installed leaders in the Kherson and Zaporizhzhya regions push ahead with their threatened referendums on joining Russia.
The U.S. State Department said the filtration operations are "an apparent effort to change the demographic makeup of parts of Ukraine."
In Kherson, civilians with pro-Ukrainian views are being detained en masse, said Natalia Yaschuk, an executive at Euromaidan SOS.
That could prevent them from taking part in any referendum, helping generate an outcome that suits Moscow. The data and documents gathered could also be used to falsify the poll's results.
Levashina's story ended on a happy note. A Mariupol rabbi intervened to get her to Ukrainian-controlled territory and, from there, to Israel.
Meanwhile, Oleksandr and his family eventually made their way to the European Union via Russia.
However, the emotional scars of their ordeals will remain with them.
As for those missing since they entered filtration centers, their whereabouts may not be known until the occupied territories are liberated, said Yaschuk.