Traditional viruses were computer programs with static structure exhibiting very limited functionality. Once identified for the first time, their structure is utilized by antivirus (AV) software as a tool for detecting the similar viruses with similar patterns. However, modern viruses are smart enough to self-configure and even change the pattern of their functionality making it hard for AV software detecting them. A polymorphic virus is a complicated computer virus that affects data types and functions making it difficult to inspect its internal structure. In this paper, we conduct a study of the polymorphic virus to answer three research questions: (1) What are the general techniques employed by these viruses to exhibit polymorphism? (2) What is the state-of-the-art of detecting polymorphic viruses? And (3) What should be made to help antivirus software detect these viruses? The result of this study may provide a good source of knowledge for polymorphic researchers and anti-virus software company getting the overall picture of this virus and thus provides a suitable solution to the problem.