BRUTE FORCE DIVERSITY. “Although a high mutation rate is dangerous for a virus because it results in nonviable individuals, it has been hypothesized that high mutation rates create a ‘cloud’ of potentially beneficial mutations at the population level, which afford the viral quasispecies a greater probability to evolve and adapt to new environments and challenges during infection.”
http://www.nature.com/nature/journal/v439/n7074/abs/nature04388.html