In this episode the Russian mafia is interested in email spam to obtain sensible personal information of Bank customers. The mafia also threatens Don and his family.
During the show, Charlie and Amita tried to find the ones who emptied Don's accounts by following the flow of information in the Internet. But how is the information in the Internet transmitted? The process of selecting paths in a network to send date is called routing. There are many algorithms used to make this process "efficient" (depending on what one means by efficient) For instance, if one thinks of a network as a directed graph where there is a weight assigned to its edges (you can think of the weight of an edge (u,v) as being the number of seconds that it takes to transmit information between u and v) it is conceivable that we might be interested in finding the fastest way to provide information from a source to all the other vertices (routers) in the network.
There exist an algorithm to solve this problem: Dijkstra's
algorithm.
We describe this algorithm:
In the episode Charlie tried to use game theory to understand Yuri Koverchenko's reasons to hack into Don's bank accounts. Here we briefly explain some ideas of game theory. Game Theory considers situations where at least two people (aka players) are involved. Each player's decisions influence the outcome of a certain event in a way which is spelled out in the rules of the game. Depending on which event actually occurs, the players receive a reward (which could be money). Usually the players will not agree on what event should occur, and thus have different goals when playing (like the FBI and the Russian mob). We now focus on matrix games, where one player wins what the others loose. Games like ticktacktoe, bridge, poker, chess, go, and others can be put in the form of matrix games, although they are too complicated to be completely analyzed (otherwise, it would not be fun to play them!)
Consider the following game: There are two players, A and B. Player
A is given a black 5 and a red 5, while player B is given a red 2, a
red 3, and a black 5. The rules are the following: both players know
what cards were given to the other; they pick one card and show it to each other at the same time. If both players
pick cards of the same color, player B must pay player A the difference
between the numerical values of the cards. On the other hand, if they
pick cards of different colors, player A pays the (positive) difference
between the numerical values of the cards.
We can summarise the payout rules with the following table
B chooses red 2 
B chooses red 3 
B chooses black 5 

A chooses red 5 
(3,3) 
(2,2) 
(0,0) 
A chooses black 5 
(3,3) 
(2,2) 
(0,0) 
where (a,b) means that player A gets a dollars (if a<0, player A
owns B a dollars) and player B gets b dollars (if b<0, player B owns A b dollars).
One would expect the players to choose the option that yields the highest reward. In B's case, this is choosing red 2. But A could easily expect player B to do just that! On the other hand, it is more convenient for A to choose the red card, since then he cannot loose any money. Similarly, if B picks black 5, he won't win anything, but he won't loose either.
B 
B 

A 
(0,0) 
(15,15) 
A 
(1,1) 
(5,5) 