When Google issued its stunning charge earlier this week that it had been subjected to cyber attacks by China, it did not spell out who or what institutions were responsible for the attack. However, security firm VeriSign says it has a good idea.

"Sources indicate that they believe the attack is the work of actors operating on behalf of or in the direct employ of official intelligence entities of the People's Republic of China. Two independent, anonymous iDefense sources in the defense contracting and intelligence consulting community confirmed that both the source IPs and drop server of the attack correspond to a single foreign entity consisting either of agents of the Chinese state or proxies thereof," VeriSign (NASDAQ: VRSN) said in a release.

In the wake of the attacks, which Google (NASDAQ: GOOG) said included attempts to hack the Gmail accounts of Chinese human rights advocates, the search giant said it plans to pull out of the Chinese market unless it can work out a way to offer uncensored search results in the country. The Chinese government insists that all Web companies abide by its censorship rules, which limit coverage of certain topics.

In Google's blog post announcing its decision, the company said its investigation revealed that at least twenty other large companies, including those in Internet, finance, technology, media, and chemical sectors, were similarly targeted. VeriSign said it believes more than 30 firms were hit, including many high-tech firms based in Silicon Valley and it added defense contractors to the sectors named.

Without elaborating, the iDefense statement said that the attack was "in many cases successful." Google said the specific effort to access Gmail accounts failed, but it has since hardened the security infrastructure of the popular e-mail service.

"Google reports that it identified malicious code on its system in mid-December. Sources say that Google then followed the code back to the drop servers, and determined that in addition to the compromise of its own systems, the attack hit an additional 33 companies," iDefense said.

Adobe (NASDAQ: ADBE) said in a blog post earlier this week that it recently became aware of a sophisticated, coordinated attack against corporate network systems managed by Adobe and other companies.

"At this time, we have no evidence to indicate that any sensitive information - including customer, financial, employee, or any other sensitive data - has been compromised," Adobe said in its post. "We anticipate the full investigation will take quite some time to complete."

Yesterday, U.S. Secretary of State Hillary Clinton issued the following statement on Google's announcement:

"We have been briefed by Google on these allegations, which raise very serious concerns and questions. We look to the Chinese government for an explanation. The ability to operate with confidence in cyberspace is critical in a modern society and economy. I will be giving an address next week on the centrality of Internet freedom in the 21st century, and we will have further comment on this matter as the facts become clear."

David Needle is West Coast bureau chief at InternetNews.com, the news service of Internet.com, the network for technology professionals.