There does exist a possibly vulnerability in Russia's nuclear system. Do a little research about 'dead hand' and you will see that it might be possible to design something that would duplicate a 'command rocket' signal that launches other missiles.
Generally speaking, all it takes to steak someone's identity is having their name, Social Security Number, and birth date. I thought I was relatively safe in giving out my SSN to questionably-secure companies that I do business with (ex. satellite tv) so long as I don't have to give them my DOB. Well a week ago I discovered that it is, in fact quite easy to get someone's DOB depending on where they live. In my state, the Judicial Branch maintains a website where you can search for municipal, superior & supreme court case information by first and last name, and the search results reveal the FULL BIRTHDATE of the plaintif and defendant for EVERY CASE INCLUDING SPEEDING AND PHOTO RADAR TICKETS! I found mine for a speeding ticket I plead guilty to back in 1996 and the birthday was correct.
Promptness is its own reward, if one lives by the clock instead of the sword.