line services. Finally, in January 2010, Google indicated it wasn’t willing to censor search results and was considering pulling out of China.

After a series of hacker attacks originating from China in February and unsuccessful negotiations with the Chinese government, Google closed its China search site and began rerouting searches from China through its Hong Kong site. However, any searches conducted from China come back censored. While many applauded the decision to halt censored service in China, Google also was criticized by Chinese officials and citizens.

In fact, no nation has received as much public scrutiny as China and its so-called “Great Firewall.” Only a few fiber-optic cables—think of them as checkpoints—manage data flowing into the country. Nevertheless, 99% of content flows through untouched, Lih says. In most instances, there’s no easy or definable way to determine exactly what’s being blocked and what citizens can access.

That’s because China, like many
countries, blocks sites sporadically and
in no systematic way. “For one thing,
there’s no official policy or admission
that the practice is taking place in
China. For another, there’s no docu-
mentation,” Lih says. The net effect for
those browsing the Web or attempt-
ing to connect to a blocked service is
a “Connection Reset” message that
the requested Web page or service is
unavailable. “It looks as though you’ve
encountered technical difficulties or a
temporary disruption,” Lih says.

Nanotechnology
Molecular
‘Robots’
Advance
How Censorship Works

Governments’ techniques for denying access to online information include:

Doman Name Service block

Name lookup fails or an internet service provider redirects it to another site.

Internet Protocol (IP) block

This approach forbids packets to a specific host based on ip address. it usually results in a “timed out” error message.

Uniform Resource Locator (URL) keyword block

a sensitive word or specific context contained in the destination web page triggers a UrL block. images and links may fail to load. This occurs frequently when using Google and other search engines.

Web content keyword triggers block

specific keywords result a “Connection interrupted” error. These blocks are often temporary and difficult to replicate. They appear to be a technical internet problem.

a multidisciplinary team from Columbia University, arizona state University, the University of Michigan, and the California institute of Technology (Caltech) have created and programmed “robots” the size of a single molecule that can independently move across a nano-scale track. First reported in Nature, the development marks an important advancement in the fields of molecular computing and robotics, and could contribute to the development of molecular robots that can sense their environment, repair individual human cells, or assemble nanotechnology products.

The project was led by Milan N. stojanovic, a faculty member in the division of experimental therapeutics at Columbia University, and included erik winfree, associate professor of computer science at Caltech; hao Yan, professor of chemistry and biochemistry at arizona state University; and Nils G. walter, professor of chemistry at the University of Michigan in ann arbor.

in recent years, scientists have worked to create robots that can reliably perform useful tasks, but at a molecular level. This involves reprogramming dNa molecules to perform in specific ways, and often involves “researchers at the interface of computer science, chemistry, biology, and engineering,” says Mitra basu, a program director at the National science Foundation, which partially funded the project.

Now, stojanovic’s research team has created molecular robotic “spiders” that can move autonomously through a two-dimensional landscape and act in basic robotic ways, demonstrating that they are capable of starting motion, walking, turning, and stopping.

while the field of molecular robotics is just emerging, it is possible these tiny devices may have important medical applications. “This work one day may lead to effective control of chronic diseases such as diabetes or cancer,” basu says.