It’s good you’re using a better encryption method than WEP, but you chose a weak encryption key. Just because the encryption is better doesn’t mean the key can’t be cracked…. Always use strong passwords and keys – at least eight characters while including upper case, lower case, numbers and symbols.
As an example, a six character password using upper and lower case and numbers can be cracked by brute force within about ten minutes using a normal modern computer. By comparison, an eight character password using the same criteria and computer would take approximately twenty-five days. Toss in symbols and an eight character password will be pretty tough to crack in a reasonable amount of time.
Read more about picking the right password in this article.