DrFPGA: wind river has built an embedded hypervisor(which is a pretty good way to secure applications against malware) , in 10K lines of code. I don't know what micruim has, but lines of code is not a good way to judge it.
@Rick, the growth numbers for Micrium were interesting. Do you know if they are from developers moving up from programming to bare metal or dropping back from more-complex Linux environments? My bet would be on the former.