Disinfecting software is not very accurate, for a variety of reasons. The error rates are fairly high; however, most are soft errors. This is a result of incomplete information regarding the virus and the lack of quality assurance among virus writers. Additionally, removal techniques tend to fail when a system or file has been infected multiple times (i.e., by the same virus more than once, or by more than one virus).
These programs are relatively easy to use and can disinfect large numbers of programs in a very short time. Any system overhead is inconsequential since the system should not be used until the virus is removed.