n Just as a human virus is passed from person from person, a computer virus is passed from computer to computer. n A virus can be attached to any file that you copy to your computer.If you download files from the Internet or copy programs or files from friends on floppy disks, you are very susceptible to a viruses. n Many viruses are spread from s. Sometimes you don’t have to download the file from the to get a virus, you can get it by just opening the itself. n A virus becomes active when you execute a program that contains a virus. For example, if you download a program from the Internet and it is infected with a virus, the virus will attack your computer when you activate the program.

Nonresident viruses are thought of as consisting a finder module and a replication module. The finder module will look for the files to infect then it will call on to the replication module to infect the file. Resident viruses contains a replication module that is similar to one that is in a nonresident virus. But the module is not called a finder module. Instead the replication module is loaded into the memory. Resident viruses are catergorized into fast either fast infectors and slow infectors. Fast infectors are designed to infect as many files as possible and slow infectors are designed to infect infrequently. The disadvantage to the fast infectors is that it is more noticeable and easier to detect. And the disadvantage to to slow infectors is that the approach does not seem very successful.

There are four different ways to prevent viruses. Self-modification is the most modern antivirus program. It scans from viruses with virus signatures. If it can find a pattern in a file that relates to a virus signature it will notify the user that the file is infected. Some viruses though can make detection by means of signatures very difficult but not impossible. Some viruses modify their code on each infection. Encryption using a variable key is more advanced than the use of a simple encryption because it enciphers the virus. The virus in this case would consist of a small decrypting module and an encrypted code of the virus. If the virus uses a different encrypted key for each infected file then the only the decrypting module remains constant. Which would be destroyed in the end. In this case instead of detecting for virus signatures the computer looks for the decrypting module.

Polymorphic code was the first technique that posed a threat towards virus scanners. A polymorphic virus infects files by making an encrypted copy of itself, which is deconded by a decryption module. The difference between a polymorphic virus and a encryption virus is that the decrypting module changes with each infection as well, therefore no parts are identical between infections making it very hard to detect. Some viruses that employ a polymorphic code mutate the rate of the virus significantly. The advantage of using the slow polymorphic code because it is hard to obtain a sample of them for the anti-virus professionals because bait files that are infected in one run will typically contain identical or similar samples of the virus. Metamorphic viruses rewrite themselves completely. To enable metamorphism you need a metamorphic engine. The metamorphic virus tends to be very large and complex.

n Viruses - A virus is a small piece of software that piggybacks on real programs. For example, a virus might attach itself to a program such as a spreadsheet program. Each time the spreadsheet program runs, the virus runs, too, and it has the chance to reproduce by attaching to other programs. n Trojan horses - A Trojan horse is simply a computer program. The program claims to do one thing but instead does damage when you run it.Trojan horses have no way to replicate automatically. n Worms - A worm is a small piece of software that uses computer network and security holes to replicate itself. A copy of the worm scans the network for another machine that has a specific security hole. It copies itself to the new machine using the security hole, and then starts replicating from there, as well.

n The trigger that activates the product can be anything. The virus can be activated the minute it is installed. Or in the other hand, it may start up the next time you open your computer. n The virus usually reside in your computer in an inactive state, waiting for a certain event to happen. n A virus can wait patiently in your system and attack only on certain date or time.

Viruses are connected to e-commerce because viruses can affect your business and consumers. It affects businesses because it can erase files and important data from the website and company. It affects consumers because sometimes viruses will show as a pop- up ad or a an advertisement and once you click on it the virus will affect your computer. Business can not always prevent these but the major corporations will usually go to great measures to ensure their customers safety.

n New Viruses are written everyday,Companies like McAfee, Symantec and Panda Software are constantly Looking for new viruses and updating their antivirus software tools. n Having a strong and updated virus protection program will complement and help excel your company by not having malfunctions or any frauds happening in your site. n Some anti-virus software update automatically and some you have to do it your self by going to there site. Over all you should update your software, its not worth having viruses in your computer or your server.