Recently some of the major antivirus software makers have announced the release of the first virus that infects the applications that run on both Windows and Linux systems. The virus was named W32,Winux, Linux or W32/Lindose and it can be transported in executable files in both Windows and Linux. After running an infected application the virus is broadcasted to other executable files from the same directory. This Czech virus, unlike Melissa and Loveletter virus doesn't intended to be transmitted via email.
Most viruses that we know are for Microsoft operating systems. But what about other operating systems like UNIX? It is commonly believed that there are no viruses or trojans in the UNIX operating system, but how valid is this claim?
For those that are not familiar with the UNIX operating system, we can introduce the topic by noting that this has become the commonly used operating system for multi-user environments and heterogeneous, due to their flexibility in communications, adaptation to different architectures and integration capability.
The structure of the executable programs on these operating systems, make them susceptible to be attacked by computer viruses. UNIX's executable files have three sections that can be attacked by the viruses: the header, the text segment and the data segment.
Previously, the executable programs of this system, were containing the code and the initialized data per process, the new version have a distinct possibility called “Shared Libraries”, that are working quite well. The library can be used by different programs. While this new features brings many advantages, it also offers a good opportunity for virus writers. Although there is no virus that can exploit this feature yet, the "shared libraries" would give the possibility to infect the working environment without the need to attack each particular file. Just putting corrupt code in a shared library, that library would activate the virus whenever it is loaded into the various programs.
The fact that there are more viruses, trojans, worms and backdoors in Windows environment should be much closer to the fact that most virus writers know them better. We can say that as far as the UNIX system become more accessible, we shall see more and more viruses on this platform. The aim of the ones who create computer viruses is to do damage, so they concentrate on the most widespread systems.