There have been cases where a person working in the bank will "hack" into the system and change how the system handles interest so that fractions of a cent are transferred into an account of that intruder. Active intruders are also sometimes responsible for denial of service attacks. Recently, there was an attack on the 13 DNS servers that store all of the name information for the Internet. Although not enough servers were affected to the point that the traffic on the Internet suffered, this was definitely a malicious attack to disrupt global communications.
There are several ways to prevent crackers from doing harm to or reading data. This technology is known as cryptography. The basics behind cryptography is to change how something appears so others cannot see what it is. Changing plaintext to ciphertext using monoalphabetic substitution is an example of this. .
abcdefghijklmnopqrstuvwxyz.
to.
qwertyuiopasdfghjklzxcvbnm.
A more sophisticated way of encrypting data is known as public key encryption. This uses a set of two keys, a public key (that is published) and a private key (that is kept secret). The data is encrypted using the public key (that is known to everyone) and decrypted by the private key. Behind the scenes of this type of cryptography, the data is encrypted and decrypted using a set of mathematical algorithms. For example, given a certain amount of time, paper and a pencil, most people could calculate.
314159265358978 times 314159265358978. However, most people given the same materials could not calculate the square route of 3912571506419387090594828508241 which happens to be equal to the numbers used in the first equation. This is the basis for public key encryption. This becomes extremely difficult to decipher when there are hundreds of numbers involved. This is why it is widely used in the cryptographic world.
Securing the machines themselves is slightly different. While encrypting data may work for the most part, there is still a slight chance that an invader could find some information on the system and manipulate it.
