A recent TV program showed how easy it was for another person to view your browsing the internet whilst using a wireless connection. What softwear is available to scramble you signal
What Chuck said, although in order for to actually be properly secure make sure you use a strong password. This involves using a password with at least 8 characters, not an actual word, and one that includes letters - preferably both upper and lower case - numbers and also a special character such as an @ symbol.
If you use a password that's easily guessed, your level of encryption security is severely lessened.