Legal experts are split in their evaluation of Google's defense strategy in two copyright-infringement lawsuits, particularly regarding the company's arm-twisting attempts to extract confidential information from uninvolved competitors.

Some view Google's tactics as aggressive, unusual and ultimately ineffective, while others see them as part of a fairly standard defense in copyright litigation.

Google sent subpoenas to Amazon.com, Yahoo and Microsoft demanding they provide it with information about their book-scanning activities, a move that raised eyebrows because those companies are among its biggest rivals. Google plans to use this information in its defense in two lawsuits filed last year. The suits allege that Google's massive project to scan, make searchable and store digital copies of millions of copyrighted library books without permission from the copyright owner is illegal. Google is also scanning books in the public domain.

Google argues that its scanning is protected under the fair use principle, which allows for limited use of copyright material, because it only displays text snippets of copyrighted books' content in response to queries in its Book Search service.

That overall argument, along with the subpoena tactic, demonstrates Google is willing to mount an atypical and pugnacious defense, said Lee Bromberg, a partner at Bromberg & Sunstein LLP, a firm that specializes in intellectual property litigation. "This [subpoena action] isn't par for the course at all in this type of case," he said.

With the subpoenas, Google is trying to argue that if its competitors are scanning books, it follows that Google is acting legally, according to Bromberg. "But I don't think it's evidence of that at all, and I think it's out of line for Google to do this," Bromberg said.

This type of subpoena is usually used to get evidence from an uninvolved third party that may have relevant information about the litigation. For example, it would make sense for Google to subpoena information from one of its business partners, or from a partner of one of the plaintiffs, Bromberg said.

"Those partners might possess documents that could be relevant to sorting out the issues between Google and the plaintiff publishers here. But that doesn't seem to be the case," Bromberg said.

Wendy Seltzer, a Fellow at the Harvard University Law School's Berkman Center for Internet & Society and an expert on Internet law and intellectual property, said the subpoenas might be part of a more conventional defense, in which Google will try to prove that book-scanning isn't hurting copyright owners nor the publishing market. Google's ultimate goal will be to have the court say its activities are protected by the fair use principle, which allows for limited use of copyright material, she said.

Already Yahoo and Amazon.com have refused to comply with the subpoenas and have indicated in court filings that they are determined to stand their ground against what they consider an inappropriate and overreaching request from Google. Microsoft declined to comment when asked how it has responded or plans to respond to the subpoena.

What's clear is that the subpoena standoff could further complicate and lengthen an already complex case that, barring an unexpected settlement, could drag on for years.

After the refusals from Yahoo and Amazon.com, the ball is in Google's court. Google has the option to file a motion with the court to compel its two rivals to comply with the subpoena request. If the court were to grant that motion to compel, Amazon.com and Yahoo would probably have a choice to escalate the matter to an appeals court.