Why is it I can't "piggyback" and get internet in my area, and someone else I know can?

They can obtain internet service by reception from someone else's computer. Anyway, I tried to do the same thing and they want a "Security Key" to "PiggyBack" off of them. The other person didn't need a security key. I don't know what the security key is so how am I supposed to override that so I can get internet as well?