I think we should be looking within the rocks, not underneath them. From a NASA policy paper on Mars (2009):
"Direct evidence of life might not beeverywhere on the surface (the premise of the Viking) but biosignatures could still
be present, within the rocks at shallow depth."
http://mepag.nasa.gov/decadal/JohnFMustarda.pdf
Life within rocks = endoliths
http://en.wikipedia.org/wiki/Endolith
So, they drilled into a rock. Now they're having a press conference. Gee, I wonder what they might have found?