Just as in January, computer hackers based in China are being accused of cyber espionage and the Chinese government is denying involvement and calling the charges groundless.

In January, the targets were Google, dozens of other companies, and the e-mail accounts of human rights activists. Following revelations about the incident, Google said it would stop censoring search results in China, a decision that led the company recently to redirect queries from mainland China to Google servers in Hong Kong.

This time, the targets are the Indian Ministry of Defense, the United Nations, and the Office of the Dalai Lama, among other organizations.

There's a noteworthy difference in the two attacks, however: The security experts who revealed the attacks managed to track the perpetrators over eight months.

As a consequence, the researchers were able to obtain copies of various sensitive and classified documents from the hackers. These documents included files taken from governments, businesses, academic institutions and other entities.

Some of the stolen data consisted of visa applications provided to Indian embassies, for example. Other data recovered included some 1,500 letters sent from the Dalai Lama's office between January 2009 and November 2009.

The researchers said they handled the sensitive files responsibly and notified affected organizations.

The report on the attack, published by Information Warfare Monitor -- made up of Citizen Lab, part of the Munk School of Global Affairs at the University of Toronto, and the SecDev Group -- and the Shadowserver Foundation, is called Shadows in the Cloud: An investigation into Cyber Espionage 2.0.

The authors of the report contributed to a similar investigation last year called GhostNet that found circumstantial evidence pointing to attackers located in China.

The "Espionage 2.0" designation represents an attempt to differentiate between previous hacking methods and an emerging approach that relies on "the misuse of social networking and cloud computing platforms, including Google, Baidu, Yahoo, and Twitter, in addition to traditional command and control servers."

The researchers identified three Twitter accounts, five Yahoo Mail accounts, twelve Google Groups accounts, eight Blogspot blogs, nine Baidu blogs, one Google Sites account, and 16 blog.com blogs that were part of the attackers' infrastructure.

The malware used to compromise victims typically involved an element of social engineering, to convince recipients to open infected files. The attackers used PDF, PPT, and DOC files to exploit old and recent vulnerabilities in Adobe Acrobat and Acrobat Reader, Microsoft Word 2003 and Microsoft PowerPoint 2003.

The report concludes by warning that the selling points of cloud computing -- reliability, distribution, and redundancy -- are the very properties that make cloud services attractive to cybercriminals.

"Clouds provide criminals and espionage networks with convenient cover, tiered defenses, redundancy, cheap hosting and conveniently distributed command and control architectures," the report says. "They also provide a stealthy and very powerful mode of infiltrating targets who have become accustomed to clicking on links and opening PDFs and other documents as naturally as opening an office door. What is required now is a much greater refection on what it will take, in terms of personal computing, corporate responsibility and government policy, to acculturate a greater sensibility around cloud security."