Once they capture the Fob signature it's just like having a key fob for that vehicle.
Anyone with a keyless start type vehicle should always store their key fob's in a faraday cage when at home. If you don't this is how easy it is to steal your vehicle.
You can look up what a Faraday cage is here: Faraday cage - Wikipedia
It's easy to build your own or you can purchase one for not allot.
The automotive industry needs to come up with a fix for this.

Cheers
Willy