Acceptance testing is a means by which software is verified to be ``virus-free'' before it is put into daily use. This is usually accomplished by placing the software on an isolated system and performing tests that are intended to mimic every day use. A combination of anti-virus tools is required to adequately perform this function, which must detect both known and future viruses. In particular, a checksum program is most useful. Even if the trigger conditions for the payload are not met, the virus will still most likely attempt to replicate. It is the result of the replication process that a checksum program detects.