But generally, the pest detection rates of anti-virus software are quite low. Neither product fared well against our test suite. They do not normally examine the registry nor make changes to it. They do not reconfigure the machine to ensure that they run at next boot. The challenge with a virus is to remove it from the objects it has infected, returning them to a fully functional state.
Trojans often do install themselves in a machine.
They often modify the registry, and sometimes also modify .ini files, such as win.ini. Deleting a Trojan will cause a problem if the registry calls for a missing file to be run. Unlike virus removal, removing a Trojan may require editing the registry. To detect a Trojan with a scan string is not difficult. To do so without false alarming on other non-Trojans is difficult.