Google has plugged a security hole that exposed the vast majority of Android phone users' calendars and contacts when they accessed those services over unsecured networks.

"Today we're starting to roll out a fix which addresses a potential security flaw that could, under certain circumstances, allow a third party access to data available in calendar and contacts," a company spokesman wrote in an email. "This fix requires no action from users and will roll out globally over the next few days."

The server-side fix addresses an implementation error in earlier versions of Android, which is used by more than 99 percent of those using the mobile operating system, according to Google figures. Versions 2.3.3 and earlier failed to transmit authentication tokens over an encrypted channels.

Attackers monitoring Wi-Fi hotspots and other open networks could exploit the weakness by copying the so-called authTokens and using them to gain unauthorized access to users' Google Calendars and Contacts.

The vulnerability could also cause devices synchronizing with Google Picasa web albums to transmit sensitive data through unencrypted channels, academic researchers from Germany's University of Ulm said.

The Google spokesman said the company's security team is still investigating those claims.

The fix forces Google servers to use an encrypted https connection when phones sync with Calendar and Contacts. ®