In the smartphone-patent wars, the forces lining up against Android—namely, Microsoft and Apple—are hoping Android has one particular Achilles' heel. The hoped-for weakness is that their use of "standards essential" patents will somehow prove very problematic: that courts won't allow them to use such patents in litigation, that they can only be licensed for very low values, or that the government will object to their use all together.

In legal papers filed at the International Trade Commission uncovered yesterday, Apple revealed Samsung is being investigated by the Department of Justice over possible antitrust issues tied to the company's use of standards-essential patents. That's in addition to an investigation being conducted by European regulators, which was already revealed earlier this year.

The DOJ investigation has been going on for several months, according to a source close to the investigation who spoke to the Wall Street Journal.

Google and its subsidiary Motorola are already being looked at by DOJ lawyers and European authorities over the same issues.

If the use of standards-essential patents in lawsuits is ultimately frowned on by government regulators, that will be a major problem for Google and its Android partners. They have tended to rely on those types of patents to hit back against patent attacks from competitors. In the recent Apple v. Samsung trial, Samsung tried to counter-attack with standards-based patents—and was allowed to ask for big damages based on them. But ultimately the tactic was unsuccessful.

Next month, Microsoft is scheduled to square off with Motorola. The two will meet in a Seattle federal court for a trial to decide how much Motorola will be able to demand for its standard-essential patents.