Posted by arlene

Computer viruses have been around for a long time. These are programs that travel from one computer to another, using various methods, such as programs that are not what they appear to be. Shareware downloaded from the Internet is a popular method for spreading virus code. You really should seriously enforce a policy for any programs that are installed on any computer in your network. Even software applications from a known vendor should be tested vigorously in a laboratory setting before being deployed on host computers in the network. Shareware, of course, should be evaluated much more closely. Regardless of any policy you decide to implement, it should be clear that viruses are particularly dangerous and sometimes tricky to avoid. The use of antivirus software is a must and should be required protection on any size network where infiltration and data destruction is undesirable—and that includes just about every network, doesn’t it?

Trojan horses are programs that an intruder plants on one or more servers in your network. If you have these types of programs, they can be difficult to detect, because many use the same filename as a file that is already part of your operating system or application software. The Trojan horse program is activated by some specific event, such as the arrival of a certain date, or by a user running a program that has been replaced by the Trojan horse. This latter tactic is very popular. Some programs are not what they appear to be.

Worms are usually considered to be self-propagating programs that travel through email as well as by other means. A worm will replicate itself by sending copies of the software to all or most of the addresses in your email address book. A worm travels through the Internet very quickly because of this aspect of its replication. The solution? Don’t open email attachments unless you have a good antivirus program (which you have kept up-to-date). After you open an email that contains a worm virus, all heck can break loose, and the friends in hour address book will not be inclined to think very well of you!

Other types of destructive programs can attack your network. This is the case in a denial-of-service attack. The perpetrators never have to intrude into your network. Instead, they use one of several methods (which we’ll talk about in just a minute) to send massive amounts of network traffic to your network router or server. The server or router becomes overwhelmed and can no longer operate efficiently. Other denial-of-service attacks target specific resources, such as servers or applications.

Trojan Horse Programs

Trojan horses are programs that are planted somewhere in your network to wait for a signal before springing into action. After hackers have gained entry to a server in your network, they can easily plant a program and then run the program, at a time they choose. The program can listen on a selected port waiting for a signal. The program can wait until a certain time has passed. Many methods are used to trigger such a program.

When the signal or time comes, the Trojan horse does its destructive chores. One of the most common techniques for hiding these programs is to give them the same name as some other common program on the computer. Indeed, some Trojan horses are nothing more than modified versions of astandard operating-system file. So what appears to be one thing might be something entirely different. As mentioned earlier, a Trojan horse program also can be activated by other means. The main difference between a Trojan horse program (or a worm) and a computer virus is that the virus is usually activated, does its damage, and then attempts to replicate itself by some means, such as mailing itself to everyone in your address book. Trojan horses are more like bombs waiting to go off.

Computer Viruses

Computer viruses come in all sorts of variations. They have been wreaking havoc on computers even before the Internet became commercial. Before the Internet exploded into the large network it is today, bulletin board services were a popular method for exchanging files, such as shareware programs.

A virus program usually is distinguished by two features. First, the virus replicates itself so that it can be spread to other computers. The method of transport can be a floppy disk that has had its boot sector code modified, or it can be a macrovirus that comes as part of an email attachment that uses the Internet email system to move about. Second, a virus usually is created to do something destructive, such as wiping out the contents of a hard disk or damaging some other system resource. However,this second feature is not always present in a computer virus. Some viruses simply display a silly message on the screen to let the user know he’s been hit, and then they do no further damage.

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