On the evening of March 31, Aleksandr Markov heard the doorbell and rushed to open the door of his St. Petersburg apartment. But instead of the guest he had been expecting, Markov was surprised to see several strangers on his doorstep.
Then came the blow.
"I was hit in the eye," he tells RFE/RL. "I found myself in the staircase. Someone pushed me from behind and I fell over. They started kicking me."
The assailants fled the scene only after Markov screamed for someone to call the police.
The incident is one of the latest in what appears to be a string of assaults and arson attacks targeting Russians who have openly criticized their government on social-networking sites.
Markov co-administers an opposition group called Criminal Authorities on VKontakte, Russia's largest social network. The group has about 14,000 members and openly denounces Kremlin policies, including those pertaining to Ukraine.
"Since November, there has clearly been a deepening crackdown on what people are writing, especially on VKontakte," says Andrei Soldatov, a noted Russian security expert. "It's obvious that VKontakte is under close scrutiny."
In addition to being assaulted, Markov has also been harassed online for weeks. A VKontakte account recently created under the name Aleksandr Petrogradsky offers to send viewers detailed information about him.
Meanwhile, Markov's brother has received a threatening message from an anonymous user.
"We have long talked about Aleksandr Markov, a former DJ at a gay club," the message reads. "Sometimes he's beaten up. When will normal guys finally see this 'artwork.' (sic) I know three of them, but they are currently on an expedition. They said they will return and deprive Markov of something that will never grow back."
Soldatov says online freedoms have been under threat in Russia since the adoption of tough legislation regulating the Internet, dubbed by some the "blacklist law" and passed early in Vladimir Putin's third term as president, in 2012. Although authorities insist that the legislation is aimed at combating child pornography and websites that promote drug use and teen suicides, its critics say the law is being used to enforce government censorship over the Internet.
In December, a blogger was sentenced to five years in a Siberian jail after he criticized Russia's military intervention in Ukraine on videos he posted VKontakte and YouTube. Vadim Tyumentsev was also barred from publishing any content online after serving his sentence.
Rafis Kashapov, an activist from Tatarstan, was also jailed for three years in 2015 for denouncing Russia's support of separatists in eastern Ukraine and its illegal annexation of Crimea in online posts.
The latest jailing came in May, when Andrei Bubeyev was sentenced to two years and three months in prison for two reposts critical of authorities -- one an article titled Crimea Is Ukraine and the other an image showing a toothpaste tube with the words "Squeeze Russia out of yourself."
Physical violence against Internet users, however, has only recently emerged as a new trend. Observers have suggested the assailants are either acting at someone else's behest or are lone wolves emboldened by the repressive new Internet legislation.
"For the first three years, the system was based on intimidation, on suspended sentences," says Soldatov. "Since last November, there have been a series of real sentences, people are being sent to prison just for sharing images. So repressions for what people write on social networks are definitely intensifying."
Another administrator of Criminal Authorities on VKontakte, Yegor Alekseyev, was assaulted on June 9.
Alekseyev, who also lives in St. Petersburg, says two men crept up from behind as he walked down a quiet street and beat him up for about five minutes. They did not steal anything. He suffered a broken nose, a concussion, and a skull fracture.
Alekseyev says he believes that his assailants knew his schedule and itinerary, and that the attack was carefully planned by individuals with special training.
He says he has been receiving e-mail and phone threats for the past three years over his involvement in the dissident group on VKontakte.
At least one more person connected to the group, Yulia -- who declines to give her surname for safety reasons -- has recently suffered unpleasant incidents that she believes are retaliation for her online activities.
A St. Petersburg resident who regularly contributes posts to the group, Yulia received a suspicious visit in mid-April. Two men showed up at her front door, told her they were her new neighbors, and said something about a store that was going to open up in her building.
The pair struck her as dubious, but she thought nothing of it until her car was torched overnight a few weeks later.
She shared her story on VKontakte and posted pictures of the two men who had showed up at her door. The friend whom Markov had been expecting on March 31 identified them as the same men he had seen exiting Markov's building after the attack.
Yulia stresses that she has no connection to Markov and Alekseyev other than their involvement in the Criminal Authorities group.
"They weren't on my friends list, we weren't members of the same [online] groups," she tells RFE/RL. "We have completely different backgrounds with no links to each other."
Shortly before her car was burned down, Yulia also discovered that her name was mentioned in several disparaging comments published on an unfamiliar VKontakte account.
The posts mostly criticized her opposition views. The account was registered under the name Aleksandr Aleksandrov and featured a photograph of her husband as its avatar. An unknown user had posted several photographs of Yulia's husband taken outside their home.
The account was deleted after Yulia filed a complaint with VKontakte.
While there is currently no evidence that the attacks are politically motivated, the list of people who have landed in trouble after publishing posts critical of authorities is growing quickly.
In January, Danila Aleksandrov, an opposition activist, received a greeting on VKontakte from a user registered as Aleksandrov Danila-Abu-Ilyas.
The fake account contained a series of covert photos of Aleksandrov showing him walking his dog. Nine days later, after receiving the ominous message, Aleksandrov was assaulted in the street and beaten up. He was hospitalized for one week.
On April 20, the wife of Ruslan Starostin received a friend request from an unknown VKontakte member calling himself Yevgeny Krestovsky. The account initially used a picture of Starostin and his wife as its profile photo.
The anonymous user shared one of Starostin's own posts -- an image poking fun at Putin -- accompanied by a threat. "You think you can freely take the piss, rally giggling morons around you, and get away with it?" the comment said.
Several hours later, Starostin's car was torched.
The latest suspicious assault came on June 12, when unidentified men attacked a VKontakte employee known for his occasional antigovernment posts.
The attackers broke three of his fingers and called their victim a "traitor," a "Jew," and a member of the "fifth column" -- a term frequently used by Russian state media to describe the opposition.