A Skype bug that enables an attacker to bypass the lock screen on several Android mobile devices demonstrates once again the need for additional security to protect corporate data against such flaws, experts say."Pulser," the developer administrator for XDA-Developers Forum, reported the bug in Skype version 18.104.22.16873, which was released on Monday. Skype is installed on more than 100 million Android devices worldwide, says Microsoft, which acquired the messaging platform in 2011.To exploit the flaw, the victim's phone or tablet would need to have Skype turned on and the attacker would then have to call from another account, prompting the device to display the green answer button.When the button is tapped to accept the call, the attacker would then hang up. Turning off the receiving device through the power button and turning it back on would end with the lock screen being bypassed until the gadget is rebooted.Pulser successfully tested the bug on the Sony Experia Z, the Samsung Galaxy Note 2 and the Huawei Premia 4G.Microsoft said in a statement on Wednesday: "We are investigating claims of an issue involving Skype for Android and will take actions as necessary to help protect customers."Lock screen-bypass bugs are not uncommon. A similar vulnerability was found in the Skype rival Viper in April, Ars Technica reported. The flaw affected smartphones made by Samsung, Sony and HTC.In March, Samsung's configuration of the emergency call function in its Android phones made it possible to unlock the devices. Terence Eden, a U.K.-based developer community manager, first reported the flaw with InMobi, a mobile advertising agency.[Slide show:\u00a010 tips for Android security]"I'm actually surprised that we keep finding lock-screen vulnerabilities that are exploited by third-party applications," Lee Cocking, vice president of strategy for mobile security firm Fixmo, said Tuesday of the latest flaw. "To me this speaks of overall security architecture issues with the platform, or at least with how background processes such as VoIP (Voice over IP) applications interact with the platform."Jack E. Gold, an analyst with J. Gold Associates, said the recurring lock-screen problem demonstrates the need for additional layers of security on mobile devices that carry corporate data. This is critical when employees use their own devices for work."The best approach is to segregate business apps and data from consumer apps with some form of virtualization or containers that isolate the corporate side of things," he said.Examples of vendors that provide virtualization technology to isolate corporate from personal data include VMWare and Enterproid. Vendors that provide container architectures include Mocana, Good Technology and Fixmo."The old adage that layered security is better than relying on a single wall of security is true here," Gold said. "The lock screen should be just one layer of the goal to protect enterprise data."Francois Lascelles, a product architect for Layer 7, agreed that the lock screen should never be trusted by itself, on any device. "Built-in device lock has been shown to be easily cracked on all major mobile platforms," he said.