By following these steps, ne'er-do-wells can unlock the phone without knowing your passcode, giving them full access to your phone and the data contained inside it.
Phone fan Scott Reed has posted a video detailing how it's done: type in a sequence of numbers until a menu appears, choose a certain option and boom -- the phone is unlocked.
Not having an Xperia Z in the office, we haven't tested whether we can recreate the problem, but I did contact Sony for more information. Sadly the company has yet to respond and let me know when we can expect an update fixing the security flaw.
Sony has recently issued a software update for the Xperia Z to solve problems with the phone suddenly shutting down, so it's clearly aware of problems.
Glitches that let you get round the lock screen have affected a number of phones lately, particularly the Samsung Galaxy S3, which can be also be unlocked simply by pressing a certain sequence of buttons -- that one we did verify. Samsung has yet to issue an update to fix the problem.
The Apple iPhone has also had problems with the lock screen after the update to iOS 6.1 software.
To see what all the fuss is about with the Xperia Z, press play for a handsome hirsute chap giving the phone a dunking:
Have you caught some Z? Is Sony experiencing a renaissance with the latest Xperia? Tell me your thoughts in the comments or on our Facebook page.