The Foneros have to log in with their FON account to get any wireless past the start page (and a single site, that you can configure yourself). Who logs in where is logged, and you get an overview on your FON account page who made use of your router, when, and how long. As such, it is secure: there is a 'paper trail' to track down if anything unsavoury happens over your wifi signal.
You can check the FON maps to get an idea of the FON spots in/near your usual haunts.
This is an especially nice deal if you don't already have a wireless router at home, but EUR 20 for free wifi almost everywhere is sweet too. So if you want an invite, just let me know!