Is it time for some lead underpants?

A few weeks ago I was riding to work and noticed my bike computer was going wild. I was stopped. The computer was telling me I was going 99.9 km/h. This, of course, was doing wonders for my average speed. I started looking around and noticed that there was a UPS truck just in front of me. What kind of invisible waves of death were circling the UPS truck. Is there a higher incidence of sterility in UPS delivery people? I was generally worried for the person in the truck. None-the-less I carried on, vowing never to stop beside a UPS truck again.
Then it happened again. I was at a stop light and my cycle computer was going mad. Now I have to admit I didn't spend a lot on this particular computer. I think it was ~$20.00, and it is wireless. I have really no idea how these computers work, but I suspect it is something like this. The magnet on the wheel trips a switch in the sender unit, some magical pulse is created and sent to the receiving unit in the computer. The computer calculates the speed based on the number of these pulses that it gets. OK that's enough technical jargon. Anyway, I realised that in my attempt to have the traffic light to change by standing with my bike over the sensor in the road I was actually standing in a large magnetic field. It was this magnetic field that was over powering my computer.

Is this something cyclists should be worried about? Should I be wearing lead underwear? What about a tinfoil hat? Thank goodness I have already had kids!