During its Atmosphere conference on cloud computing that's  being held in Paris this week, Google announced plans to make its Google Apps offering more secure by adding two-step authentication.

Security is believed to be the No. 1 concern facing businesses that are contemplating moving their data, applications, or both to the cloud. Cloud providers are attempting to quell these concerns by adding security technology to their offerings, hoping to convince customers that data stored in the cloud is just as secure as if it was stored in house.

For its part, Google this week is beefing up the security of its Google Apps Premier, Education, and Government Edition by giving administrators the option of having their users sign in with both a password and a one-time verification code that is provided to them via mobile phone.

Google is pitching two-step authentication as more secure than passwords alone, but not as complex or costly as other security measures.

"For the first time, we're making it possible for organizations large and small to use this technology in just a few clicks for free," wrote Eran Feigenbaum, Director of Security at Google Apps, in a Monday blog post.  "In the coming months, we'll also be offering this same security to our hundreds of millions of individual Google users."

The verification code is sent to users via SMS, a voice call, or an app that can be installed on Android, BlackBerry, or iPhone devices, says Feigenbaum. By requiring this second form of authentication, intruders can no longer gain unauthorized access to data or applications with simply a password. Users can turn off the requirement for the second form of authentication by indicating that they are using a trusted computer, says Feigenbaum.

Google says its two-form authentication will integrate with other vendors' technologies. The free security enhancement will be available to users of Google Apps Standard Edition in the coming months.