computer virus
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malicious code.[citation needed]PDFs can also be infected with malicious code.
In operating systems that use file extensions to determine program associations (such as Microsoft Windows), the extensions may be hidden from the user by default. This makes it possible to create a file that is of a different type than it appears to the user. For example, an executable may be created named “picture.png.exe”, in which the user sees only “picture.png” and therefore assumes that this file is an image and most likely is safe.
An additional method is to generate the virus code from parts of existing operating system files by using the CRC16/CRC32 data. The initial code can be quite small (tens of bytes) and unpack a fairly large virus. This is analogous to a biological “prion” in the way it works but is vulnerable to signature based detection.
This attack has not
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