On March 14th, online security journalist Brian Krebs was cleaning his Virginia home in preparation for a small dinner party when he noticed some plastic tape stuck under his front door, left over from when he’d had to secure an extension cord. Pulling up the tape, he opened the front door — and suddenly heard a yell. "Don’t move!" the voice said. "Put your hands in the air!" There were around 10 to 12 police officers surrounding his driveway, guns drawn.

Fortunately, Krebs realized immediately what had happened. He had actually warned the police months before about the possibility of a fake emergency call designed to bring a SWAT team to his house, an increasingly popular prank among the young hackers he writes about. Still, he was shaken.

"Any time people who are trained to respond to hostile situations show up at your door pointing automatic weapons at you, things can go wrong very easily," Krebs told The Verge. "I'm a pretty cool customer, as these things go, but when they said ‘put your hands up,’ I had a big huge ball of tape in my hands. What if somebody mistook that for a weapon?"

Heavily armored special police units were a common sight in the Boston metro area last week during the hunt for the bombers who attacked the Boston Marathon. But special forces had been seeing more action than usual, across the country and before the bombings, thanks to an old prank known as "swatting" that’s recently come back into style.

Back in January, police received a 911 call about a husband threatening his wife with a gun. After sweeping the property and startling the handful of staffers who were the only ones home, it became obvious that the call was a hoax. The victim? R&B singer Chris Brown.

Tom Cruise, Kim Kardashian, and others have also been unnecessarily visited by a SWAT team. In February, actor Clint Eastwood got the SWAT treatment. In March, Paris Hilton was hit. Selena Gomez, Justin Timberlake, Russell Brand, and Rihanna were all swatted in the same week in the beginning of April. The problem is so bad that the LAPD has stopped publishing reports of swatting incidents in order to discourage copycats.

So far, one swatter has been caught: a 12-year-old boy who admitted to swatting Ashton Kutcher, Justin Bieber, and a bank. The Los Angeles County District Attorney also says the boy called 911 once to get out of school.

The attacks have been happening outside Hollywood as well. North Carolina-based Woody, a vlogger who runs a YouTube channel called WoodysGamertag, was dramatically swatted in March. Woody had just wrapped up an episode when he noticed people prowling around in his yard, so he came down the stairs with a shotgun — which is just about the most dangerous reaction you can have in that situation.

"I’m what my wife describes as a minor league internet celebrity," Woody said in a video. "It turns out the ultimate goal of these swatters, I’m told, is to have them bust through the door and drag you off camera. They would just love to see the police grab me by my shoulders and pull me off the show."

The FBI estimates there are around 400 swatting attacks a year, based on "local law enforcement calls received about once a month; interviews of individuals arrested; and a review of social media with perpetrators bragging about it," a spokesperson told The Verge. However, Google Trends shows a huge spike in mentions of the word "swatting" beginning in 2013.

It’s relatively easy to swat someone, since law enforcement tends to err on the side of taking emergency calls seriously. The threshold for calling in a special forces team varies by district, but generally it seems to be enough to say you have a gun and a potential victim. All swatters really need is the victim’s address, a way to mask their phone number, and a crazy story to tell the 911 operator.

There are a few options when it comes to masking your phone number. Swatters can use services designed so the deaf can type and have their messages spoken by an operator. Because of privacy laws, these services do not track personal information of the people making the calls, and the operators are required to read everything that’s being typed, no matter how absurd. Swatters can also use a "spoof card," magicJack, or even an app (Burner is a popular one) to hide the originating number.

As it turns out, the recent increase in swatting may be connected to one specific hacker, or group of hackers. Krebs discovered that an individual, or individuals, has been publishing personal information on public figures on a site called exposed.re. At the end of March, a notation was added next to the names of celebrities who had been targeted: "[Swatted]."

"I actually think there is a connection between the swat against me and the swat against celebrities," he said. The FBI is investigating the case.

Swatting can bring harsh penalties. In 2007, a young man named Randal T. Ellis called in a hoax on an apparently random household using a deaf relay service. At first, Ellis told the 911 operator that his name was Ryan and his sister had overdosed on cocaine and gave the address of a house in Lake Forest, Washington, where Doug and Stacey Bates lived with their twin daughters. Ellis also claimed he had a gun and had shot someone in the face. He then threatened to shoot his mother and his sister.

At this point, police requested a SWAT team. Doug Bates heard a strange noise and saw some the shadowy figures in the yard. Worried about intruders, he came out the back door with a knife.

Excerpt from 911 transcript:

[Police unit 664] confirming these people are deaf ? we may need to get someone out here that speaks sign language

[Sheriff’s dispatch] Six six four we’re still trying to confirm that. We do have an informant by the name of Ryan. He states he shot a female in the face

[Police unit 664] – He’s at the back window, he’s looking out. And ah – it looks like he does have a large knife in his hand and he is agitated. He’s coming out.

Luckily, no one was hurt in the ensuing standoff. The police searched the Bates’ home and found nothing. "Fuck this bullshit, I'm just going to kill myself," Ellis told the 911 operator, and hung up.

At the time no law enforcement had ever heard of swatting, Sims told The Verge. The only other case he was aware of involved Matthew Weigman, the notorious blind phone hacker who ended up getting 11 years for various computer crimes. Weigman’s first known swat was in 2005. The Verge attempted to contact Weigman to ask whether he was inspired by an earlier swat, but he declined to be interviewed through his lawyer.

Sims is now consulting with the LAPD to help with the string of Hollywood swats. "Unfortunately for us, with the new spoof cards and the magicJacks, and everything else coming out, it’s becoming more and more difficult," he said. "It’s very labor intensive. It’s not like you got swatted last night and I can have someone in custody today."

However, he said, the swatters tend to give themselves away. "It’s almost like a high for them," he said. "They want to memorialize all this activity, all this news media. They’re only going to stay quiet for so long."

Update: Woody asked that his real name be removed from this story in order to reduce his future risk of being targeted, so we substituted his nickname.