A Steiner Chain is a set of n circles, all of which are tangent to two given non-intersecting circles, where n is finite and each circle in the chain is tangent to the previous and next circles in the chain. In the usual closed Steiner chains, the first and last circles are also tangent to each other; by contrast, in open Steiner chains, they need not be. The given circles do not intersect, but otherwise are unconstrained; the smaller circle may lie completely inside or outside of the larger circle. In these cases, the centers of Steiner-chain circles lie on an ellipse or a heyperbola, respectively. Facebook

A small area deep in the brain called the perirhinal cortex is critical for forming unconscious conceptual memories, researchers at the UC Davis Center for Mind and Brain have found.


The perirhinal cortex was thought to be involved, like the neighboring hippocampus, in "declarative" or conscious memories, but the new results show that the picture is more complex, said lead author Wei-chun Wang, a graduate student at UC Davis.
The results were published Dec. 9 in the journal Neuron.

We're all familiar with memories that rise from the unconscious mind. Imagine looking at a beach scene, said Wang. A little later, someone mentions surfing, and the beach scene pops back into your head.

Declarative memories, in contrast, are those where we recall being on that beach and watching that surf competition: "I remember being there."

Damage to a structure called the hippocampus affects such declarative "I remember" memories, but not conceptual memories, Wang said. Neuroscientists had previously thought the same was true for the perirhinal cortex, which is located immediately next to the hippocampus.
Wang and colleagues carried out memory tests on people diagnosed with amnesia, who had known damage to the perirhinal cortex or other brain areas. They also carried out functional magnetic resonance imaging (fMRI) scans of healthy volunteers while they performed memory tests.

In a typical test, they gave the subjects a long list of words, such as chair, table or spoon, and asked them to think about how pleasant they were.

Later, they asked the subjects to think up words in different categories, such as "furniture."
Amnesiacs with damage to the perirhinal cortex performed poorly on the tests, while the same brain area lit up in fMRI scans of the healthy control subjects.

The study helps us understand how memories are assembled in the brain and how different types of brain damage might impair memory, Wang said. For example, Alzheimer's disease often attacks the hippocampus and perirhinal cortex before other brain areas.
Co-authors on the study are Andy Yonelinas, professor of psychology and at the Center for Mind and Brain; Charan Ranganath, professor at the Center for Neuroscience; former UC Davis graduate student Michele Lazzara, now project coordinator at the University of Illinois at Chicago; and Robert Knight, professor of psychology at UC Berkeley. The work was funded by the National Institutes of Health.

The Web surfing history saved in your Web browser can be accessed without your permission. JavaScript code deployed by real websites and online advertising providers use browser vulnerabilities to determine which sites you have and have not visited, according to new research from computer scientists at the University of California, San Diego.

"JavaScript is a great thing, it allows things like Gmail and Google Maps and a whole bunch of Web 2.0 applications; but it also opens up a lot of security vulnerabilities. We want to let the broad public know that history sniffing is possible, it actually happens out there, and that there are a lot of people vulnerable to this attack," said UC San Diego computer science professor Sorin Lerner.
The researchers documented JavaScript code secretly collecting browsing histories of Web users through "history sniffing" and sending that information across the network. While history sniffing and its potential implications for privacy violation have been discussed and demonstrated, the new work provides the first empirical analysis of history sniffing on the real Web.
"Nobody knew if anyone on the Internet was using history sniffing to get at users' private browsing history. What we were able to show is that the answer is yes," said UC San Diego computer science professor Hovav Shacham.
The computer scientists from the UC San Diego Jacobs School of Engineering presented this work in October at the 2010 ACM Conference on Computer and Communications Security (CCS 2010) in a paper entitled, "An Empirical Study of Privacy-Violating Information Flows in JavaScript Web Applications."

History Sniffing

History sniffing takes place without your knowledge or permission and relies on the fact that browsers display links to sites you've visited differently than ones you haven't: by default, visited links are purple, unvisited links blue. History sniffing JavaScript code running on a Web page checks to see if your browser displays links to specific URLs as blue or purple.
History sniffing can be used by website owners to learn which competitor sites visitors have or have not been to. History sniffing can also be deployed by advertising companies looking to build user profiles, or by online criminals collecting information for future phishing attacks. Learning what banking site you visit, for example, suggests which fake banking page to serve up during a phishing attack aimed at collecting your bank account login information.
"JavaScript is a great thing, it allows things like Gmail and Google Maps and a whole bunch of Web 2.0 applications; but it also opens up a lot of security vulnerabilities. We want to let the broad public know that history sniffing is possible, it actually happens out there, and that there are a lot of people vulnerable to this attack," said UC San Diego computer science professor Sorin Lerner.
The latest versions of Firefox, Chrome, and Safari now block the history sniffing attacks the computer scientists monitored. Internet Explorer, however, does not currently defend against history sniffing. In addition, anyone using anything but the latest versions of the patched browsers is also vulnerable.

Sniffing out History Sniffing

"We built a dynamic data flow engine for JavaScript to track history sniffing in the wild. I don't know of any other practical tool that can be used to do this kind of extensive study," said Dongseok Jang, the UC San Diego computer science Ph.D. student who developed the JavaScript monitoring technology. The researchers plan to broaden their work and study what information is being leaked by applications on social media and other Web 2.0 sites.
The computer scientists looked for history sniffing on the front pages of the top 50,000 websites, according to Alexa global website rankings. They found that 485 of the top 50,000 sites inspect style properties that can be used to infer the browser's history. Out of 485 sites, 63 transferred the browser's history to the network. "We confirmed that 46 of them are actually doing history sniffing, one of these sites being in the Alexa global top 100," the UC San Diego computer scientists write in the CCS 2010 paper.
Table 1 in the paper outlines the websites the computer scientists found that performed history sniffing during the data collection period. In some cases, the websites created their own history sniffing systems. In other cases, advertisements served by outside companies contained JavaScript code performing the history sniffing.

History Sniffing in Perspective

The computer scientists say that history sniffing does not pose as great a risk to your privacy or identity as malicious software programs (malware) that can steal your banking information or your entire Facebook profile. But, according to Shacham, "history sniffing is unusual in effectively allowing any site you visit to learn about your browsing habits on any other site, regardless if the two sites have any business relationship."

To see history sniffing in action, visit: www.whattheinternetknowsaboutyou.com
"I think people who have updated or switched browsers should now worry about things other than history sniffing, like keeping their Flash plug-in up to date so they don't get exploited. But that doesn't mean that the companies that have engaged in history sniffing for the currently 60 percent of the user population that is vulnerable to it should get a free pass," said Shacham.

Tracking History Sniffing

The UC San Diego history-sniffing detection tool analyzes the JavaScript running on the page to identify and tag all instances where the browser history is being checked. The way the system tags each of these potential history tracking events can be compared to the ink or paint packets that banks add to bags of money being stolen.
"As soon as a JavaScript tries to look at the color of a link, we immediately put 'paint' on that. Some sites collected that information but never sent it over the network, so there was all this 'paint' inside the browser. But in other cases, we observed 'paint' being sent over the network, indicating that history sniffing is going on," explained Lerner. The computer scientists only considered it history sniffing when the browser history information was sent over the network to a server.
"We detected when browser history is looked at, collected on the browser and sent on the network from the browser to their servers. What servers then do with that information is speculation," said Lerner.
The "paint" tracking approach to monitoring JavaScript could be useful for more than just history sniffing, Lerner explained. "It could be useful for understanding what information is being leaked by applications on Web 2.0 sites. Many of these apps use a lot of JavaScript."

You know when you're watching a pirated film downloaded from the Internet -- there's no mistaking the fuzzy footage, or the guy in the front row getting up for popcorn. Despite the poor quality, pirated video is a serious problem around the world. Criminal copyright infringement occurs on a massive scale over the Internet, costing the film industry -- and the U.S. economy -- billions of dollars annually.

Now Dr. Alex Bronstein of Tel Aviv University's Department of Electrical Engineering has a new way to stop video pirates. With his twin brother Michael and Israeli researcher Prof. Ron Kimmel, he has developed the ultimate solution: treating video footage like DNA.
Sequencing the video genome
"It's not only members of the animal and plant kingdom that can have DNA," says Dr. Bronstein, who was inspired by DNA sequencing tools used in bioinformatics laboratories. "If a DNA test can identify and catch criminals, we thought that a similar code might be applicable to video. If the code were copied and changed, we'd catch it."
Of course, video does not have a real genetic code like members of the animal kingdom, so Dr. Bronstein and his team created a DNA analogue, like a unique fingerprint, that can be applied to video files. The result is a unique DNA fingerprint for each individual movie anywhere on the planet.
When scenes are altered, colors changed, or film is bootlegged on a camera at the movie theatre, the film can be tracked and traced on the Internet, explains Dr. Bronstein. And, like the films, video thieves can be tracked and caught.
The technology employs an invisible sequence and series of grids applied over the film, turning the footage into a series of numbers. The tool can then scan the content of Web sites where pirated films are believed to be offered, pinpointing subsequent mutations of the original.
The technique is called "video DNA matching." It detects aberrations in pirated video in the same way that biologists detect mutations in the genetic code to determine, for example, an individual's family connections. The technique works by identifying features of the film that remain basically unchanged by typical color and resolution manipulations, and geometric transformations. It's effective even with border changes, commercials added or scenes edited out.
Finding a common onscreen ancestry
The researchers have set their sights on popular video-sharing web sites like YouTube. YouTube, they say, automates the detection of copyright infringement to some degree, but their technique doesn't work when the video has been altered.
The problem with catching bootlegged and pirated video is that it requires thousands of man-hours to watch the content being downloaded. Production companies know their only hope in recouping stolen content is by automating the process. "Video DNA" can provide a more accurate and useful form of this automation.