New viral environments are discovered each year. Over the last 20 years of PC viruses, there has been tremendous dark energy in place to develop computer viruses for almost every platform imaginable. All over the world, thousands of people created computer viruses. Because of this we are experiencing an ever-growing security problem with malicious code and, consequently, seeing the development of computer virus research as a new scientific field. There is absolutely no question whether computer viruses will stay with us and evolve to future platforms in the upcoming decades.
Fred Cohen's initial research with computer viruses in 1984 concluded that the computer virus problem is ultimately an integrity problem. Over the last 20 years, the scope of integrity expanded dramatically from file integrity to the integrity of applications and operating system software. Modern computer viruses, such as W32/CodeRed and W32/Slammer, clearly indicate this new era: Computer viruses cannot be controlled by file-based integrity checking alone because they jump from system to system over the network, injecting themselves into new process address spaces in such a way that they are never stored on the disk.
Computer viruses changing their environments to suit their needs is a problem that will likely begin to emerge. For example, the W32/Perrun virus appends itself to JPEG picture files. Normally, pictures files are not infectious unless some serious vulnerability condition exists in a picture file viewer (such as the one described in Microsoft Security Bulletin MS04-02855). However, Perrun modifies the environment of the infected host to include an extractor component, resulting in Perrun-compromised JPEG files not being infectious on a clean system but on infected computers only. Such computer viruses can modify the host's environment in such a way that previous assumptions about the environments no longer hold.