Two months after exposing a scandal involving sex tapes, blackmail and lucrative government contracts, which resulted in 11 officials losing their jobs, blogger Zhu Ruifeng received a surprise visit from Chinese security officials Sunday night.

“They are standing outside my door right now, knocking and even kicking the door, telling me to open it,” he said in a frantic phone call to a reporter.

As he talked, men could be heard shouting in the background. “I think they’re coming to take me away,” Zhu said. “I talked to too many in the media, and it must have irritated someone.”

The late-night standoff at Zhu’s home lasted more than two hours, ending when he promised to show up Monday morning at a nearby police station. And it illustrates the perils and possible limits of an anti-corruption campaign launched in November by China’s new leaders.

Experts and citizens have questioned whether the effort will have any lasting results or is merely a show to stem increasing disenchantment with the ruling Communist Party.

Lei Zhengfu, center, a former Chongqing official, was fired after blogger Zhu Ruifeng released a graphic video showing Lei having sex with an 18-year-old girl. (Chen yuanhong/Imagine China)

Most reports of corruption have come from online whistleblowers, such as Zhu, who post their findings on China’s Twitter-like microblogs, known as weibo. Some bloggers had hoped the anti-corruption drive would help them avoid the harsh government reprisals they have experienced in the past.

But many are increasingly quoting an ancient saying once used to describe the execution of criminals and now a reference to the party’s long, unforgiving memory: “Wait to settle your scores until after the autumn harvest.”

If local authorities are allowed to punish whistleblowers, experts warn, the anti-corruption campaign will lose what little momentum it has gained in the past two months.

And of all the scandals exposed since the effort began, Zhu’s was the most salacious and high-profile.

A self-described “independent investigative journalist” based in Beijing, Zhu released a graphic video, filmed about five years ago, showing a local party boss in the metropolis of Chongqing having sex with his 18-year-old mistress.

Thevideo of Lei Zhengfu, 57, soon went viral as a symbol of party corruption, and Lei was fired within days.

But many details of the case were kept under wraps until Friday, when government-run media announced the removal of 10 more party officials.

According to reports in Chinese media, including state-run CCTV, property developers, in a plot to extort construction contracts from Chongqing officials, paid young women to videotape themselves having sex with the officials.

After he released the video, Zhu remained relatively unscathed. He said he received two death threats from people he thinks were associates of Lei but was left alone by authorities. In a November interview, he said he had five more sex tapes depicting other officials with young women that he was waiting to release.

At that time, Zhu said his experience had given him some hope for reform. “In the past, I’ve encountered a lot of threats, censorship and even kidnapping, but this time, my Web site wasn’t shut down. There was no blocking or attack,” he said. “I think maybe the sky really is changing.”

On Sunday night, he was rethinking his position.

Police had searched for him first at another home where he has occasionally stayed, frightening family members. Then they arrived at his door.

The men said they had come from a local Beijing security station, but Zhu suspected that they were from Chongqing and that their intent was to take him away and recover the five additional sex tapes he had threatened to release.

Recently, he said, a source told him that Chongqing authorities had destroyed all other recordings related to the ex­tortion case in an attempted coverup, leaving only the video Zhu had made public.

Zhu said he then transferred the unreleased videos to friends in the United States, which he called “the safest place in the world.” The videos, he noted, include officials who have not been punished or fired.

“If something bad happens to me, I hope my friends will release those videos immediately,” he said.

Subsequent calls to Zhu on Sunday night went unanswered, but he posted a message online saying that police had agreed to meet him and his lawyer at the station Monday morning and that they had left minders at his home.

In later posts, media professor Zhan Jiang said he had checked on Zhu at his home, and lawyer Wang Peng said he visited Zhu and saw a police car with Beijing plates stationed outside.

“If tomorrow I still end up being taken away by Chongqing policemen,” Zhu said in his last message of the night, “I hope all of you will continue supporting me.”

That post was quickly deleted, apparently by censors.

Wang Juan in Shanghai contributed to this report.