In the new Infiniti G, you can set this option.
Do you want just the Driver's door to unlock, or all four, when the driver's handle is touched.
It an option that can be set in the settings menu through the NAV display.
I'd be surprised if the IS doesn't have this same option, even if it's one that is set by the dealer.
Personally, I prefer the Driver's door only.
Again, the security issue is only a concern for some people. In the case of “lambobaby1218” it appears that she is not given the option to open one or all four doors. It is a loss of control that could bother some people. However I hope that no one ever finds out the hard way. In this case, the potential intruder does not need to have perfect timing as the original post stated that door unlock automatically without the passenger handle being triggered.
The Lexus Personalized Settings allows some options when using the key fob buttons on the remote. Basically you can choose to open only the driver’s door or all four doors with either one or two presses of the unlock button. Having the option to choose is what is important.
In my case both my wife and I carry the key fobs when entering the vehicle. So we can both gain access without delay. The system can do a good job of detecting multiple key fobs.