A security flaw in Skype version 18.104.22.16873 could enable a thief or hacker to get around your Android lockscreen, according to a report in ThreatPost.. The exploit was found by xda-developer member Pulser, who tested it on the Sony Xperia Z, Samsung Galaxy Note 2 and Huawei’s Premia 4G.
The exploit requires the attacker to have two phones with Skype and initiate a call between the two handsets. Once a call is in progress, the caller hangs up and the lockscreen appears on the recipient’s phone. The attacker then turns off the recipient phone, turns it back on again. This simple on/off trick will bypass the lockscreen and give the attacker full access to the device. The lockscreen will remain bypassed until the phone is rebooted.
You can read more about the flaw in this thread on Full Disclosure.