Americans suddenly fearful that the U.S. government can easily find out who they are telephoning have software options to disguise their calling records.

But information specialists say that if the government really wants to get the information, it likely can get it in the end.

The Obama administration on Thursday defended its collection of millions of telephone records as part of its counterterrorism efforts.

That came after Britain's Guardian newspaper published a secret court order authorizing the collection of phone records generated by Verizon Communications customers.

Experts say that while there are plenty of services that can make a phone number anonymous, or mask where someone is calling from, the government can still get most of the data it wants with relative ease.

"It's really hard to feel as if you have complete confidence that you are untraceable," said Justin Brookman, director of Center for Democracy & Technology's Project on Consumer Privacy.

If a Skype user had called a Verizon user, for example, the government would see the call was made but not detect the identity of the Skype user, said Fred Cate, an Indiana University professor specializing in information privacy law.

The government could, however, request the IP address from the video and online calling service, he said.

Although there are programs that encrypt the content of phone conversations, Cate said some encrypted data can still tell the government when and to whom calls are made - just not the substance of the call itself.

In the Verizon case, the alleged court order covered each phone number dialed by customers, along with location, routing data, duration and frequency of the calls. Contents of the phone calls were not revealed.

SUBPOENA CHALLENGE

New technology is offering consumers a way to create a disposable phone number that can be deleted at any time.

Greg Cohn, CEO of Ad Hoc Labs, which developed the phone application Burner, said the application was meant to address recent challenges to mobile privacy. Users can create and delete multiple numbers, creating a privacy layer for their phones.

Vumber is a similar app. Phillip Jones, vice president of telephony solutions at AVM Software Inc., which owns Vumber, said the app is meant to protect consumers' privacy when dating or doing business, for example.

But while the phone numbers are not traceable for the average person, Jones said the company holds the information and would release it to law enforcement if requested.

Cohn also said Burner does not promise encryption. While user-to-user data is secure, the data could be provided to the government if subpoenaed.

One exception might be Silent Circle, an encrypted communications tool that allows users to speak or send messages to another user without fear of being spied on, said Vic Hyder, the company's chief operations officer.

Silent Circle generates keys on the phone devices and at the end of the conversation, the keys disappear. Hyder said there is no data to give if the government requests it.

"We're not doing anything new. This is an evolution of the technology," he said.

The Center for Democracy & Technology's Brookman said even those who go to great lengths to protect their privacy may end up leaving a trail of bread crumbs.

And by and large, "the average user isn't going to go to all this trouble," Brookman said.

(Reporting by Madeline Will; Editing by Ben Berkowitz and Xavier Briand)