Clones, robots, alien shapeshifters, or disembodied consciousness take over people's identities in shows such as Star Trek and Doctor Who. They can then take over the lives of the people they've duplicated, particularly when they have access to their memories. How can anyone defend himself when he can't tell friend from foe?
In real life, most of us don't fear having someone else show up in person claiming to be us. But we are concerned about identity theft. Our digital world makes it all too easy for the bad guys to hack into personal information posted online, as well as financial information that we can think is secure. The cost of identity theft can be huge when hackers get access to our credit cards, debit cards, and bank accounts.
Read more in Your Personal Online Guardian