A California startup behind smartphone software accused of snooping on users stepped up the defense of its creation on Friday in the face of freshly filed lawsuits.

By Friday, lawsuits had been filed in three US states against software maker Carrier IQ and smartphone manufacturers HTC and Samsung accusing the companies of breaking privacy and wiretapping laws and demanding they be made to pay.

A suit filed in a federal court in the Silicon Valley city of San Jose accused Carrier IQ of hiding "spyware" on smartphones.

Lawsuits filed against Carrier IQ in the states of Illinois and Missouri included Samsung and HTC as defendants and each sought class action status to represent everyone affected.

Damages being sought were estimated to be in the hundreds of millions of dollars.

Carrier IQ, meanwhile, received backing from a security consulting firm as it held firm that its application was a diagnostic tool for managing networks and not smartphone spy software.

"Having examined the Carrier IQ implementation it is my opinion that allegations of keystroke collection or other surveillance of mobile device user's content are erroneous," said Rebecca Bace of Infidel.

Carrier IQ asserted anew that smartphone information it captures is encrypted before being sent to mobile network operators, with whom users already have a "trusted relationship."

"We measure and summarize performance of the device to assist operators in delivering better service," Carrier IQ said in a statement.

"While a few individuals have identified that there is a great deal of information available to the Carrier IQ software inside the handset, our software does not record, store or transmit the contents of SMS messages, email, photographs, audio or video," it said.

Examples given by Carrier IQ included being able to understand whether a text message was sent accurately but not recording what was written.

"Carrier IQ is aware of various commentators alleging Carrier IQ has violated wiretap laws and we vigorously disagree with these assertions," the company said.

The software is deployed by major network operators to monitor performance and optimize efficiency, according to Carrier IQ.

"Our software allows operators to figure out why problems are occurring, why calls are dropped, and how to extend the life of the battery," Carrier IQ said.

In another development, Carrier IQ spokeswoman Mira Woods told AFP the company will respond to a request from US Senator Al Franken for specifics regarding what its smartphone software was doing.

If Carrier IQ spies on users in ways first detailed by smartphone security researcher Trevor Eckhart it could be breaking federal law, Franken said in his letter.

In a YouTube video, Eckhart showed Carrier IQ software buried deep in an Android-powered smartphone recording buttons pressed, Internet search queries, text messages and locations.

The software was tricky to find on the device and couldn't be turned off, according to his demonstration.

Another US lawmaker, Congressman Edward Markey, sent a letter to the US Federal Trade Commission chairman meanwhile saying an investigation into Carrier IQ software was warranted.