<Tr> <Td> </Td> <Td> This article includes a list of references, related reading or external links, but its sources remain unclear because it lacks inline citations . Please help to improve this article by introducing more precise citations . (March 2010) (Learn how and when to remove this template message) </Td> </Tr> <P> The Cascade virus (also known as Herbstlaub in Germany) is a prominent computer virus that was a resident written in assembly language, that was widespread in the 1980s and early 1990s . It infected . COM files and had the effect of making text on the screen cascade down and form a heap at the bottom of the screen . It was notable for using an encryption algorithm to avoid being detected . However, one could see that infected files had their size increased by 1701 or 1704 bytes . In response, IBM developed its own antivirus software . </P> <P> The virus has a number of variants . Cascade - 17Y4, which is reported to have originated in Yugoslavia, is almost identical to the most common 1704 byte variant . One byte has been changed, probably due to a random "mutation". This, however, has resulted in a "bug" in the virus . Another mutated variant is also known - it infects the same file over and over . </P>

Cascade is an example of which of the following types of virus