Examples of polymorphic viruses include HSFX virus, W95/HPS virus, W95/Marburg virus and the 1260 virus. The first polymorphic virus was the 1260 virus, which was developed by Mark Washburn in 1990 in the United States.
Polymorphic viruses are complicated computer viruses that attack computer data types and functions. Each polymorphic virus duplicates itself into millions of copies. In addition, it is able to hide itself within the files to avoid detection by the conventional computer scanners. In order to remove a polymorphic virus, program developers have to develop tools that are more aggressive than the virus itself. This means rewriting language strings to come up with scanners with very strong detection abilities. Usually, this process is not only time-consuming, but is also costly and complicated.
A person can tell when a polymorphic virus has infected a computer by detecting a change in behaviour of one or several keys. For example, if pressing the C button types another character apart from C, this is one sign of infection. When these viruses affect a computer, they may duplicate themselves or create slightly modified versions of themselves. This duplication further compounds the process or healing a computer. These viruses capitalize on the fact that most contemporary anti-virus tools are unable to detect the duplicated virus versions.