For more than three years now, Microsoft has held to the line that it has loads of patents that are infringed by Google's Android operating system. "Licensing is the solution," wrote the company's head IP honcho in 2011, explaining Microsoft's decision to sue Barnes & Noble's Android-powered Nook reader.

Microsoft has revealed a few of those patents since as it has unleashed litigation against Android device makers. But for the most part, they've remained secret. That's led to a kind of parlor game where industry observers have speculated about what patents Microsoft might be holding over Android.

That long guessing game is now over. A list of hundreds of patents that Microsoft believes entitle it to royalties over Android phones, and perhaps smartphones in general, has been published on a Chinese language website.

The patents Microsoft plans to wield against Android describe a range of technologies. They include lots of technologies developed at Microsoft, as well as patents that Microsoft acquired by participating in the Rockstar Consortium, which spent $4.5 billion on patents that were auctioned off after the Nortel bankruptcy.

The list of patents was apparently produced as part of a Chinese government antitrust review relating to Microsoft's purchase of Nokia. Microsoft described the results of that review in an April 8 blog post, writing that the Chinese Ministry of Commerce (MOFCOM) "concluded after its investigation that Microsoft holds approximately 200 patent families that are necessary to build an Android smartphone."

To suggest the lists are the "conclusion" of the Chinese government is unusual phrasing. It's unlikely anyone other than Microsoft itself would have the expertise and resources needed to sift through its thousands of patents and decide which ones they believe read on Android.

More likely, Microsoft was compelled to produce the list to appease Chinese regulators, who feared that the software giant could become more aggressive with its patents after the Nokia purchase. It seems equally likely that Microsoft wouldn't be too thrilled about the patents being published on a public webpage. In fact, the English-language version of the MOFCOM site about the merger doesn't have the patent lists.

Doing transparency, the hard way

While Microsoft's blog post talks about hundreds of patent "families," the lists published by MOFCOM make it clear that most of those "families" appear to be one-patent "households."

The Chinese agency published two lists on a Chinese-language webpage where it laid out conditions related to the approved merger. The webpage has an English version, but it doesn't include the patent lists. There's a longer list [MS Word Doc] of 310 patents and patent applications and then a shorter list [MS Word Doc] of just over 100 patents and applications that MOFCOM focused on. The shorter list appears to be a subset of the longer list, divided into families connected to Microsoft technologies like the exFAT file system and Exchange ActiveSync, denoted as patent group 24(EAS) in the short list.

The longer list is divided into three sections: 73 patents that are said to be "standard-essential patents," or SEPs, implemented in smartphones generally, followed by 127 patents that Microsoft says are implemented in Android. The final section includes another section of "non-SEP" assets, which includes 68 patent applications and 42 issued patents.

Of course, the list includes some patents that Microsoft used against Barnes & Noble, including all 14 mentioned in this 2011 Network World article. Those patents include Nos. 5,889,522 entitled "System Provided Child Window Controls," and 6,339,780 "Loading Status in a Hypermedia Browser Having a Limited Available Display Area."

It also has many newer and previously unrevealed patents, like 8,255,379 "Customer Local Search," 5,813,013 "Representing Recurring Events," and 6,999,047 "Locating and tracking a user in a wireless network through environmentally profiled data."

Notably, both the SEP section and the Android-specific section include patents that Microsoft apparently acquired when it participated in the Rockstar bid.

Rockstar paid $4.5 billion for patents belonging to Nortel. Some of those were handed off to Rockstar Consortium, a patent-licensing company that sued Android makers and Google in October. Other patents were handed off to the companies that participated in Rockstar, which included Apple, Microsoft, Blackberry, Ericsson, and Sony.

Nortel patents now owned by Microsoft include 5,982,324, which describes combining GPS with cell signals in an "efficient position location system" said to be used in Android phones. More Nortel patents are in the "general smartphone" section, such as No. 6,430,174, which describes a communication system that supports simultaneous voice and multimedia.

The patent lists are strategically significant, because Microsoft has managed to build a huge patent-licensing business by taxing Android phones without revealing what kind of legal leverage they really have over those phones. Recent estimates of its Android licensing business suggest Microsoft is earning somewhere between $1 billion and $2 billion from Android device makers paying royalties. Microsoft said last year more than 50 percent of Android devices are made by companies with licensing deals in place, and the estimates now range as high as 70 percent.

As the debate over patent reform has heated up in Congress over the past year and a half, Microsoft has said it supports bringing more transparency to the patent system. Last year, the company made a big to-do about publishing a full list of patents it owns.

But the recent publications by Chinese authorities, revelations the company likely tried to avoid, are much more indicative of what real patent transparency would look like. If large-scale licensors like Microsoft were forthcoming about what patents they believe their competitors infringe, that would create a much improved system of "public notice" about intellectual property rights. The patent system is supposed to create that "public notice" on its own, but it's sorely lacking. Patents today are written in legalese that can only be interpreted by a select tribe of professionals, and Microsoft benefits by keeping lists like this secret.

This disclosure on a foreign website, presumably compelled by the Chinese government, may produce more "transparency" about Microsoft's campaign against Android than years of unclear threats.

Asked by Ars about the lists, a Microsoft spokesman declined to comment beyond what it said in its April 8 blog post.