It sounds like it maybe a hard shutdown due to CPU overheating (some systems may even log this type of problem – check your owner manual).
Spybot uses quite a bit of CPU and usually causes systems to run at or near 100% CPU utilization for an extended period of time. If the CPU is getting too hot, the protective circuitry in the system may be shutting it down.
Some systems have marginal cooling capacity, particularly laptops. Check and make sure that your CPU fan is running and the air ducts are clean.