Security Codes:
A security code is a bunch of numbers that Apprentice rattles off to you at the beginning of each game in the format:
"Scrub's Security Code is: 4277742"
You may have no idea for what purpose they exist though. Well, we have been hiding the secret meaning of security codes for a long time but it seems time for this revelation to take place and for us to admit to the true nature of security codes -- they are for security.
What a security code is is a unique number (very unique for no two decks are alike). So lets say you are playing in an online tournament (shameless credit to www.planeswalker.com, for they are the ones holding most of the online tournaments) and your opponent disconnects due to lightning striking his pet cat fluffy (when you write the help file, you can make up the scenarios). When said player resumes the game how is his opponent supposed to know he did not change decks? Everyone now -- the security codes! This comes in handy for many things including online sealed deck and draft. So remember to record these codes, or at least watch them.