Scammers are actively exploiting a bug in Firefox that causes the browser to lock up after displaying a message warning that the computer is running a pirated version of Windows that has been hacked. The message, which appears without any any user interaction upon visiting a site, reads: Please stop and do not close the PC … The registry key of your computer is locked. Why did we block your computer? The Windows registry key is illegal. The Windows desktop is using pirated software.