[iBook] WiFi security on iBook?

[Laura Bruce]

Hi there. Interesting show on BBC3 last night exposed the vulnerablity
of computers due to their wireless internet signals. They drove a van
up outside a house, and picked up everything from the guy's ebay
purchases to his confirmation of a holiday booked online -- showing
exactly when the house would be vacant!

How vulnerable are G4 iBooks? I am running OS X 10.3.9, but wonder if
regular software updates have been sufficient to protect my computer.

My network does not require a password, and file sharing is turned off.

Ta,
Laura