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Twitter is Down. What's a "Distributed Denial of Service Attack"?

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You may have heard that Twitter, the popular social message-sharing service, was down for several hours this morning as it fell victim to a DDoS attack, or Distributed Denial of Service attack. Let's dig into what that means, from a technical perspective.

Denial of Service: It's Like Dialing the Same Phone Number Over and Over

Let's start with the basics. The simple concept behind a "Denial of Service" attack (note we're not talking distributed yet) is to overuse the service in question (for example, Twitter) to the point where it becomes unavailable to others. Think of this metaphor: if I call your home telephone over and over again, and you lack call waiting, other callers can't get through. As long as I keep calling, I'm denying service to others, thus implementing a "Denial of Service" (or DoS) attack. Now, in practice this is close to impossible with an internet service like Twitter, because, not to stretch the metaphor too far, they have a lot of phone lines. There's no way one computer could use the Twitter service so heavily that it would affect other users.

There's also the little matter that a single-line Denial of Service attack is pretty easy to defend against: you just block the offending computer (or caller, in our analogy). But things are about to get more complicated.

Let's Get Distributed

So if a standard Denial of Service attack isn't going to shut down the site, let's imagine what would happen if millions of computers began to pound on Twitter.

If a very large number of computers started hitting the service repeatedly, it could get to the point where the service became unavailable to others. When you distribute the attack among a number of attacking computers, that's called a Distributed Denial of Service Attack. That's what's happening right now. Most distributed attacks happen from computers on different networks all around the world, which makes it harder to isolate and block them. They also may look, to the server, much like normal traffic -- so it's hard to know what to block and what to let through.

But Wait...Don't Millions of People Use Twitter Every Day Anyway?

Well, yes. Twitter is designed for millions of people to constantly hit its servers, posting updates, reading others' updates, and so on. So how can it collapse under the strain of a DDoS? Well, the short answer is that a DDoS provides way more traffic than Twitter usually receives, and it's likely to be targeted on the most resource-intensive operations on the site (for example, the computers performing the attack may be constantly trying to create new accounts, reset passwords, download long lists of tweets, post new tweets over and over, or other operations that require the server to do a bit of real work).

A DDoS attack requires a lot of computers to be effective. Generally these days attackers use "botnets," or virtual armies of computers controlled by a virus, that are then centrally commanded to do something nasty -- like all hit Twitter at once. The owners of the computers generally don't even know that their computers are part of the botnet, since the virus operates invisibly in the background. The biggest botnets may well contain millions of computers, although it's hard to measure these things because the computers' owners don't know they're infected.

It's impossible to tell at this early stage who is behind the DDoS -- whether it's a prankster, an organized crime ring (these things do happen -- malicious groups have been known to threaten to DDoS a major site and hold off only when paid protection money), or even a politically-motivated group. (Can you think of an international political cause that has been linked to Twitter lately? Exactly.)

What Does Twitter Say About the Attack?

Twitter's status page contains this information (as of 10am Pacific, Thursday, August 6, 2009):

Ongoing denial-of-service attack

We are defending against a denial-of-service attack, and will update status again shortly.

Update: the site is back up, but we are continuing to defend against and recover from this attack.

Update (9:46a): As we recover, users will experience some longer load times and slowness. This includes timeouts to API clients. We're working to get back to 100% as quickly as we can.

As I type this, Twitter appears to be bouncing between "totally normal" and "bizarrely broken." Let's hope they're back and tweeting as soon as possible! For more on DDoS attacks, check out Wikipedia's Denial-of-service attack page or Understanding and surviving DDoS attacks.

You can also follow me on Twitter for more technical information, jokes, and Portland updates. Assuming Twitter is up.

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DreamWorks
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entertainment
15 Must-Watch Facts About The Ring
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DreamWorks

An urban legend about a videotape that kills its viewers seven days after they see it turns out to be true. To her increasing horror, reporter Rachel Keller (then-newcomer Naomi Watts) discovers this after her niece is one of four teenage victims, and is in a race against the clock to uncover the mystery behind the girl in the video before her and her son’s time is up.

Released 15 years ago, on October 18, 2002, The Ring began a trend of both remaking Japanese horror films in a big way, and giving you nightmares about creepy creatures crawling out of your television. Here are some facts about the film that you can feel free to pass along to anybody, guilt-free.

1. DREAMWORKS BOUGHT THE AMERICAN RIGHTS TO RINGU FOR $1 MILLION.

There were conflicting stories over how executive producer Roy Lee came to see the 1998 Japanese horror film Ringu, Hideo Nakata's adaptation of the 1991 novel Ring by Kôji Suzuki. Lee said two different friends gave him a copy of Ringu in January 2001, which he loved and immediately gave to DreamWorks executive Mark Sourian, who agreed to purchase the rights. But Lee’s close friend Mike Macari worked at Fine Line Features, which had an American remake of Ringu in development before January 2001. Macari said he showed Lee Ringu much earlier. Macari and Lee were both listed as executive producers for The Ring.

2. THE DIRECTOR FIRST SAW RINGU ON A POOR QUALITY VHS TAPE, WHICH ADDED TO ITS CREEPINESS.

Gore Verbinski had previously directed MouseHunt. He said the first time he "watched the original Ringu was on a VHS tape that was probably seven generations down. It was really poor quality, but actually that added to the mystique, especially when I realized that this was a movie about a videotape." Naomi Watts struggled to find a VHS copy of Ringu while shooting in the south of Wales. When she finally got a hold of one she watched it on a very small TV alone in her hotel room. "I remember being pretty freaked out," Watts said. "I just saw it the once, and that was enough to get me excited about doing it."

3. THE RING AND RINGU ARE ABOUT 50 PERCENT DIFFERENT.

Naomi Watts in 'The Ring'
© 2002 - DreamWorks LLC - All Rights Reserved

Verbinski estimated that, for the American version, they "changed up to 50 percent of it. The basic premise is intact, the story is intact, the ghost story, the story of Samara, the child." Storylines involving the characters having ESP, a volcano, “dream logic,” and references to “brine and goblins” were taken out.

4. IT RAINED ALMOST EVERY DAY WHEN THEY FILMED IN THE STATE OF WASHINGTON.

The weather added to the “atmosphere of dread,” according to the film's production notes. Verbinski said the setting allowed them to create an “overcast mood” of dampness and isolation.

5. THE PRODUCTION DESIGNER WAS INFLUENCED BY ANDREW WYETH.

Artist Andrew Wyeth tended to use muted, somber earth tones in his work. "In Wyeth's work, the trees are always dormant, and the colors are muted earth tones," explained production designer Tom Duffield. "It's greys, it's browns, it's somber colors; it's ripped fabrics in the windows. His work has a haunting flavor that I felt would add to the mystique of this movie, so I latched on to it."

6. THERE WERE RINGS EVERYWHERE.

The carpeting and wallpaper patterns, the circular kitchen knobs, the doctor’s sweater design, Rachel’s apartment number, and more were purposely designed with the film's title in mind.

7. WATTS AND MARTIN HENDERSON HAD A FRIENDLY INTERNATIONAL RIVALRY.

Martin Henderson and Naomi Watts star in 'The Ring' (1992)
© 2002 - DreamWorks LLC - All Rights Reserved

The New Zealand-born Henderson played Noah, Rachel’s ex-husband. Since Watts is from Australia, Henderson said that, "Between takes, we'd joke around with each other's accents and play into the whole New Zealand-Australia rivalry."

8. THE TWO WEREN’T SURE IF THE MOVIE WAS GOING TO BE SCARY ENOUGH.

After shooting some of the scenes, and not having the benefit of seeing what they'd look like once any special effects were added, Henderson and Watts worried that the final result would not be scary enough. "There were moments when Naomi and I would look at each other and say, 'This is embarrassing, people are going to laugh,'" Henderson told the BBC." You just hope that somebody makes it scary or you're going to look like an idiot!"

9. CHRIS COOPER WAS CUT FROM THE MOVIE.

Cooper played a child murderer in two scenes which were initially meant to bookend the film. He unconvincingly claimed to Rachel that he found God in the beginning, and in the end she gave him the cursed tape. Audiences at test screenings were distracted that an actor they recognized disappears for most of the film, so he was cut out entirely.

10. THEY TRIED TO GET RID OF ALL OF THE SHADOWS.

Verbinski and cinematographer Bojan Bazelli used the lack of sunlight in Washington to remove the characters’ shadows. The two wanted to keep the characters feeling as if “they’re floating a little bit, in space.”

11. THE TREE WAS NICKNAMED "LUCILLE."

The red Japanese maple tree in the cursed video was named after the famous redheaded actress Lucille Ball. The tree was fake, built out of steel tubing and plaster. The Washington wind blew it over three different times. The night they put up the tree in Los Angeles, the wind blew at 60 miles per hour and knocked Lucille over yet again. "It was very strange," said Duffield.

12. MOESKO ISLAND IS A FUNCTIONING LIGHTHOUSE.

Moesko Island Lighthouse is Yaquina Head Lighthouse, at the mouth of the Yaquina River, a mile west of Agate Beach, Oregon. The website Rachel checks, MoeskoIslandLighthouse.com, used to actually exist as a one-page website, which gave general information on the fictional place. You can read it here.

13. A WEBSITE WAS CREATED BY DREAMWORKS TO PROMOTE THE MOVIE AND ADD TO ITS MYTHOLOGY.

Before and during the theatrical release, if you logged into AnOpenLetter.com, you could read a message in white lettering against a black background warning about what happens if you watch the cursed video (you can read it here). By November 24, 2002, it was a standard official website made for the movie, set up by DreamWorks.

14. VERBINSKI DIDN’T HAVE FUN DIRECTING THE MOVIE.

“It’s no fun making a horror film," admitted Verbinski. "You get into some darker areas of the brain and after a while everything becomes a bit depressing.”

15. DAVEIGH CHASE SCARED HERSELF.

Daveigh Chase in 'The Ring'
© 2002 - DreamWorks LLC - All Rights Reserved

When Daveigh Chase, who played Samara, saw The Ring in theaters, she had to cover her eyes out of fear—of herself. Some people she met after the movie came out were also afraid of her.

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European Space Agency Releases First High-Res Land Cover Map of Africa
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Land Cover CCI, ESA

This isn’t just any image of Africa. It represents the first of its kind: a high-resolution map of the different types of land cover that are found on the continent, released by The European Space Agency, as Travel + Leisure reports.

Land cover maps depict the different physical materials that cover the Earth, whether that material is vegetation, wetlands, concrete, or sand. They can be used to track the growth of cities, assess flooding, keep tabs on environmental issues like deforestation or desertification, and more.

The newly released land cover map of Africa shows the continent at an extremely detailed resolution. Each pixel represents just 65.6 feet (20 meters) on the ground. It’s designed to help researchers model the extent of climate change across Africa, study biodiversity and natural resources, and see how land use is changing, among other applications.

Developed as part of the Climate Change Initiative (CCI) Land Cover project, the space agency gathered a full year’s worth of data from its Sentinel-2A satellite to create the map. In total, the image is made from 90 terabytes of data—180,000 images—taken between December 2015 and December 2016.

The map is so large and detailed that the space agency created its own online viewer for it. You can dive further into the image here.

And keep watch: A better map might be close at hand. In March, the ESA launched the Sentinal-2B satellite, which it says will make a global map at a 32.8 feet-per-pixel (10 meters) resolution possible.

[h/t Travel + Leisure]

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