Cyber attacks disclosed by Google and Adobe that may lead Google to quit China highlight a sophisticated type of bespoke cyberspying that could be more widespread than previously thought.

Google, the world's top search engine, said on Tuesday it might shut down its Chinese site, Google.cn, after an attack on its infrastructure it believed was primarily aimed at accessing the Google mail accounts of Chinese human rights activists.

Unlike ordinary viruses that are released into cyberspace and quickly spread from computer to computer, the type of attack launched against Google and at least 20 other companies were likely handcrafted uniquely for each targeted organization.

Such attacks, most often delivered using Adobe PDF documents sent by e-mail, secretly deposit a software file on a user's hard drive allowing the computer to be remotely accessed. Typically, top personnel with access to high-level information are targeted with such software, known as malware.

Since each organization is hit with a malware that looks different from malware delivered to others, companies cannot detect samples spreading around the globe and protect themselves as they normally would, security experts say.

Attacks like this are very hard to block and very hard to filter, says Mikko Hypponen, chief research officer at security software maker F-Secure, who has been monitoring such attacks against Chinese human-rights activists since 2005.

The fact that this kind of malware can easily sit in computers undetected, potentially forever, also means the true number of such hacking attempts is hard to estimate.

I don't think they're very unusual at all. I think they're very usual -- that's the problem, says John Walker, a professor in cyber-crime at the UK's Nottingham Trent University and chief technology officer of security software adviser Secure-Bastion.

COMPROMISED SINCE JULY?

Google said it had found that at least 20 other companies had been targeted in attacks originating from China, and that it was in the process of notifying them.

Adobe, which makes the popular Acrobat, Flash and Photoshop software including the PDF format often used by hackers, said on Wednesday its computer-network systems had been attacked, but no sensitive information was stolen.

Hypponen said the logical explanation was that hackers wanted to gain access to Adobe's development systems to better exploit PDF vulnerabilities.

Cyber security firm iDefense said that according to its sources, the attack on Google bore similarities to a July 2009 attack in which about 100 information technology-focused companies were targeted with e-mail campaigns using PDF files.

It is possible that the two attacks are one and the same, and that the organizations targeted in the Silicon Valley attacks have been compromised since July, it said.

In September, a coordinated cyberattack on the Chinese assistants of foreign news agencies contained malware that also exploited an Adobe Acrobat vulnerability.

Other companies targeted in the latest attacks did not immediately come forward.

Microsoft, which has recently launched a Chinese version of its much-hyped new search engine Bing, said in a statement: We have no indication that any of our mail properties have been compromised.

Defense contractors are other likely targets.

Last year, cyberspies that appeared to be based in China were reported to have breached the Pentagon's $300 billion Joint Strike Fighter project, using vulnerabilities in the networks of contractors involved in building the fighter jet.

The Pentagon and top supplier Lockheed Martin later said they were not aware of any specific concerns, when asked about the Wall Street Journal report.

Defense companies, facing shrinking conventional Defense budgets, are expanding into the development of ways to wage and protect themselves against cyber warfare, as the borders between consumer and Defense electronics blur.

(Additional reporting by Tim Hepher in Paris)

United kingdom Adobe Software Cybercrime