Sparse infector-logic dependence viruses
This is a type of Computer virus that only infects files when certain conditions are met.
Sparse infectors use distinct strategies to reduce their detection. They are viruses that infect “sometime”. For example, they will affect a program every tenth performance. Because they are random infectors, antivirus software has a difficult to detect them.
Strategy for Virus creation
In order to spread widely, a virus must attempt to avoid detection. To minimize the probability of its being discovered a virus could use any number of different techniques. It might, for example, only infect every 20th time a file is executed; it might only infect files whose lengths are within narrowly defined ranges or whose names begin with letters in a certain range of the alphabet. There are many other possibilities.
A virus which uses such techniques is termed a sparse infector
Sparse infector virus infects only occasionally.They will not spread as quickly but will also probably not be discovered as easily.