Scared yet? Of course you're not. This could happen to everyone else, just not you. Um... no. Read on!
Leet (or "1337") is an alternate version of the English alphabet. Leet uses symbols and numbers to replace letters.
1 = L
3 = E
3 = E
7 = T
Make sense? M@k3 53N53? Take a look at the image below.
To guess passwords, a lot of hackers use what's called a dictionary attack. In short, a program runs through an exhaustive list of common words and tests them all for a match. This type of attack has a very high success rate on passwords that use single words or variations of words found in a dictionary, such as adding a number.
To sum it all up
Bad Passwords: Password12, Secure86, Random72
Great Passwords: P@55w0rd12, 53cur386, R@nd0m72
Elite Passwords: 9@55vv02cl12, 53(y3w386, 9@/\/cl04472
Here's to being secure in 2012! I'm going to go change my password now.