In general terms, a computer virus, which is also known as "malware," refers to any computer program written with the express purpose of altering the manner in which a computer operates, without the permission of its owner. Such a bug spreads from machine to machine in much the same manner that a biological virus passes from person to person. Some viruses can lead to identity theft and wipe out important information. By definition (as imitations will not be tolerated), a computer virus requires two qualities in order to be considered bonafide: it must be able to both replicate and manage itself. Like any effective alien entity, it mutates and there are tens of thousands of them out there doing their particular damage every single day. Due to the endless variety of spreading and infection patterns, explanations must remain broad and generic.
There are many types of "malware" (malicious software) and viruses, but for the sake of clarity, we will concentrate on the six basic types. These include: file, boot sector, multipartite, macro, network and email viruses.
File viruses, which are also known as executable or parasitic viruses, are activated whenever a host program is run on the computer and can be set off immediately or via a trigger, such as a specific date. They attach themselves to files and spread by bonding with other programs within the system. If such a virus finds another program located on the drive, it will modify the programs code so that it will contain the virus the next time its run. Thus it spreads like rotten butter all across the system and into any other systems that share the infected program.
A boot sector virus affects the nerve center of the hard disk, namely where all the information about the drive is stored including the program which allows the booting up of the operating system. The bug invades every boot sequence by simply inserting its code into the boot sector. This virus usually does not affect files but spreads instead to the disks that contain them. This is why they are no longer effective threats to systems. Without floppies and with the influx of the CD-ROM, pre-written data on a CD has become impossible to infect. These viruses still exist but they are rare compared to some of the new age, malicious software lurking out there today.
Multipartite viruses are a combination of the first two, (file and boot sector) and they enter the computer through infected media, making their home in the memory sector. They first infect the boot sector of the hard drive and then spread across the system. There are not many of these viruses around today, but at one time they were a formidable enemy to every working computer due to their ability to combine different infection techniques.
Macro viruses utilize applications or programs that contain macros such as Word documents, Excel spread sheets, Power Point presentations and other similar files. These viruses present major threats because they are known to be platform-independent, that is, they can spread BETWEEN any system that is running the required application. Today, thousands of these destructive bugs exist, the very first one having been discovered back in August of 1995.
The Network virus spreads quickly across a Local Area Network (LAN) and replicates itself through shared drives and folders. Once it infects a new system, it seeks out other vulnerable systems so that they too become infected. It continues to infect until an entire network is corrupted.
The Email virus, which can be a form of a macro virus, spreads through all the contacts in the hosts email address book. If the recipient of an email from an infected address book opens an attachment, the virus spreads through his or her address book contents as well!
A computer virus is a serious thing and must be dealt with swiftly and effectively. Antivirus software is a good first line of defense against both malware and viruses. Unfortunately, viruses are not the only kind of malicious software out there as the flip side of technological advance is sometimes "technological malevolence." We must fight as Darth Vader or the Lone Ranger or even like little old Alexander Fleming who some 60 odd years ago invented penicillin by leaving his Petri dishes exposed while he went away on vacation. Where is this Nobel Prize winner now when we need him? (He may be dead, but thats no excuse.) A new wonder drug, thats what our computers need and while theres no specific rush to find it, an hour ago would be just fine!
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