Computer Viruses. Contents are

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3 Computer Viruses Contents are Introduction Types of Viruses How viruses contaminate & spread How does one determine that a computer or disk is infected? How can a virus be removed?

4 What is Virus? A virus is a "parasitic" program written intentionally to enter a computer without the user's permission or knowledge. The word parasitic is used because a virus attaches to files or "boot sectors" and replicates itself, thus continuing to spread (without your knowledge). Though some viruses do little but replicate, others can cause serious damage or affect program and system performance. A virus should never be assumed harmless and left on a system.

5 Types of Viruses Viruses are classified by their behavior in infecting computer systems: Program Viruses infect executable program files, such as those ending in.com,.exe,.ovl,.drv,.sys, or.bin. These are the files that typically start programs for you. For example, Netscape.exe starts Netscape. Boot Sector Viruses infect our Master Boot Record, FAT and Partition Table. In plain English, this means that these Viruses attack the "table of contents" on your hard drive. With a destroyed or damaged table of contents, files can be unrecoverable without professional assistance..

6 Types of Viruses (contd ) Multipartite Viruses infect both programs and boot sectors. Double trouble. Worms are virus-like programs that are primarily designed to replicate themselves, but often without infecting other files on the computer. Recent examples of viruses with worm-like behavior are the Melissa virus and the ILOVEYOU virus, which both made use of programs to send themselves out to everybody in a user's address book. Macro Viruses are transmitted in Microsoft applications that support Macros, such as Word and Excel. Macros are normally harmless little applications that a user can run in a document (say, an application that automatically calculates some values in a spreadsheet). Recently, malicious hackers have turned to using this Macro functionality to attack our computers.

7 How Viruses Contaminate and Spread A virus is typically inactive until an infected program is run or the boot record is read. As the virus is activated it loads into the computer's memory where it can perform a triggered event and/or spread itself. Disks used in an infected system can then carry the virus to another machine. Programs downloaded from bulletin boards and web sites can also spread viruses. Data files can even spread viruses, thanks to the invention of the Macro Virus..

8 How Viruses Contaminate and Spread (contd ) Boot Infecting Viruses should be of a special concern to users who share computers or floppy disks or any other storage device.. Every disk contains a boot sector whether it is a bootable disk or not. When the computer is powering up looking for the Boot information and reads an infected disk in the drive, the virus is transferred to the computer s hard drive. Once the boot code on the drive is infected, the virus will be loaded into memory every time the computer starts up. From memory the boot virus can travel to every disk that is read,, and the infection will spread. Most boot viruses could be on a system for a long time without causing problems. There are some nasty ones, however, that will destroy the boot information or erase the hard drive. Advice: do not use your floppy disk or any other storage device in a computer that does not have virus protection. You are risking your data.

9 How does one determine that a computer or disk is infected? To determine whether or not a floppy disk or computer drive is infected by a virus, it is necessary to run a virus scanning utility, a program that can detect and often remove viral code. These scanning utilities constitute the core of all anti-virus software, and every computer should be loaded with some sort of anti-virus software. Some of these programs can be made to run permanently from the computer s memory, which allows for continuous virus scanning. This solution allows for more dynamic detection and removal of viruses, especially those which enter the system through the use of floppy disks. IT Services recommends that you run anti-virus software on your machine at all times, and that you keep its virus information up to date.

10 How can a virus be removed? To remove a virus you will need to obtain an anti-virus software package; there are numerous programs available on the market, ranging in price from $30-60 (more depending on the number of updates included with the package). Such as McAfee, Norton,Avast, Quick Hill, Kasper sky etc. Most viruses are rather innocuous and can easily be detected and removed from your computer without any subsequent damage to your system. Nonetheless, it is imperative that you scan your system frequently to minimize the chance of data loss and security compromises.. Anti-virus software is covered by copyright law and is not considered shareware, hence HDS Information Technology Services will be unable to provide you with copies of such programs. You will have to obtain your own copy through a software vendor.

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