There are still too many things not being checked. Monitoring for system-level routines that perform destructive acts can help, but such monitoring is fairly easily bypassed. Do not depend on it alone. If it finds such a request, the interceptor generally pops up and asks you if you want to allow the request to continue. There is, however, no reliable way to intercept direct branches into low level code or to intercept direct input and output instructions done by the virus itself.
Some viruses even manage to disable the monitoring program itself.
Viruses have been around for twenty years, and were originally harmless. There are many types of viruses that do many things in many different ways. There are several types of virus protection available that attack viruses in three different ways. Most importantly, you can only get a virus from an infected executable file . Viruses are the cockroaches of cyberspace.