Computer Viruses and Worms

 Different types of computer virus

Virus reaserchers are, however, generally less interested in these routines because they are not significant part of the replication chain of the virus. Payloads usually represent routine programming and the technically exciting stuff is located in the replication mechanisms.

Viruses and worms

A worm, for example, is able to use services provided by a modern networked environment much more efficiently than a virus. This results in an advantage that enables worms to spread much faster than viruses.

A pure worm is more independent than a virus. A pure worm works by itself as an independent object. It does not need a carrier object to attach itself to. The worm can also spread by initiating telecommunications by itself. There is no need to wait for a human to send the file or document.

Different types of viruses

Boot sector viruses

A boot sector virus infects the boot sector of floppy disks or hard drives. These blocks contain a small computer program that participates in starting the computer. A virus can infect the system by replacing or attaching itself to these blocks.

These viruses replicate very slowly because they can only travel from one computer to another on a diskette. In addition, a boot attempt must be made on the target computer using the infected

diskette before the virus can infect it. The virus may, however, reside on the diskette and infect new computers even if there is no operating system on it. Network communications have replaced diskettes as a means of sharing data. Software is also distributed using networks or

CD-ROMs rather than diskettes. This has made the boot sector viruses almost extinct. Some boot sector viruses still remain on stored diskettes, but they are rarely activated and usually do not work in modern operating systems. However, some damage does occur because these viruses may unintentionally damage file systems that they do not understand (i.e. the NTFS file system used by Windows NT).

Traditional file viruses

This group of viruses replicates when attached to MS-DOS program files with the .EXE or .COM extensions. This group of viruses is extinct due to the fact that they rely on operating systems

that are no longer used.

Document or macro viruses

Document or macro viruses are written in a macro language. Such languages are usually included in advanced applications such as word processing and spreadsheet programs. The vast majority of known macro viruses replicate using the MS Office program suite, mainly MS Word and MS Excel, but some viruses targeting other applications are known as well.

Macro viruses differ from earlier boot sector and file viruses in many ways. Most differences are beneficial to macro viruses and enable them to spread much faster than any other kind of virus

seen thus far. The most important difference is that macro viruses infect data files rather than program files. This takes advantage of a computer environment in a much more efficient way than previous virus types. The purpose of a computer system is to store, refine and

communicate data.

Understanding the Worms