I have the software on my Nexus 5 phone. Switched the SIM card when in another country. Phone began the alarm ‘This phone has been lost or stolen’. I entered the 4 digits I remember as the password, but the bottom of the screen remained covered by the keyboard and I saw no way to hit ‘Enter’ and there was no way to proceed. The alarm continued, and the same results occurred after rebooting.
Help, please! 
→ http://www.avast.com/faq.php?article=AVKB135#artTitle (Changing a SIM card)