If Life Exists On Mars, Our Robotic Probes May Have Brought It There
http://www.spacedaily.com/news/life-01zg1.html

It includes the interesting fact that though Pathfinder was "cleaned" prior launch, it was not heat sterilized. Therefore it probably did carry some spores to Mars.
The article suggests however that the heat of reentry would probably kill such spores on the surface of the probe.
One does wonder about the interior of the spacecraft though.

The relaxing of the requirements for sterilizing Mars spacecraft was also discussed in Barry DiGregorio's article:

The dilemma of Mars sample return
http://pubs.acs.org/subscribe/journals/ci/31/special/digreg/08digregorio.html

The Spacedaily article states new methods of sterizilation rather than heating are required to protect today's sensitive electronics. Anyone know the method of sterilization used by the Beagle 2 Mars lander?

Bob Clark