THREATS TO THE COMPUTER

Introduction

One of the biggest fears of having computers are viruses, viruses are malicious programs designed entirely for destruction and havoc. Viruses are created by people who either know a lot about programming or know a lot about computers.

 Computer Virus

Computer virus is one of the greatest threats to computers and computer applications. Once the virus is made it will generally be distributed through shareware, pirated software, e-mail or other various ways of transporting data, once the virus infects someone's computer it will either start infecting other data, destroying data, overwriting data, or corrupting software. The reason that these programs are called viruses is because it is spreads like a human virus, once you have become infected either by downloading something off of the Internet or sharing software any disks or write able media that you

placed into the computer will then be infected. When that disk is put into another computer their computer is then infected, and then if that person puts files on the Internet and hundreds of people download that file they are all infected and then the process continues infecting thousands if not millions of people.

MODE OF TRANSMISSION OF COMPUTER VRUS

The majority of viruses are contract by floppy's by bringing information from one source and then put onto your computer. VIRUSES can infect disks and when that disk is put into your computer your computer will then become infected with that virus, a recent survey done in 1997 by NCSA given to 80 percent of PC users showed that 90% of PC users contract viruses by floppy diskettes.

In the survey done above it showed that the other 20% of viruses were contracted by email attachments and over the Internet. This means that you received an email with an attached file and opened the file. Or downloaded a file over the Internet.

VIRUS PROPERTIES

Your computer can be infected even if files are just copied. Because some viruses are memory resident as soon as a diskette or program is loaded into memory the virus then attaches itself into memory. Can be Polymorphic. Some viruses have the capability of modifying their code which means one virus could have various amounts of similar variants.

Can be memory / Non memory resident. Depending on the virus can be memory resident virus which first attaches itself into memory and then infects the computer. The virus can also be Non memory resident which means a program must be ran in order to infect the computer.

Can be a stealth virus. Stealth viruses will first attach itself to files on the computer and then attack the computer this causes the virus to spread more rapidly.  Viruses can carry other viruses and infect that system and also infect with the other virus as well. Because viruses are generally written by different individuals and do not infect the same locations of memory and or files this could mean multiple viruses can be stored in one file, diskette or computer.

Can make the system never show outward signs. Some viruses will hide changes made such as when infecting a file the file will stay the same size. Can stay on the computer even if the computer is formatted. Viruses have the capability of infecting different portions of the computer such as the CMOS battery or master

HOW VIRUSES MAY EFFECT FILES

Viruses can effect any files however usually attack .com, .exe, .sys, .bin, .pif or any data files. Viruses have the capability of infecting any file however will generally infect executable files or data files such as word or excel documents which are open frequently.  It can increase the files size, however this can be hidden. When infecting files virtues will generally increase the size of the file however with more sophisticated viruses these changes can be hidden.


It can delete files as the file is ran. Because most files are loaded into memory and then ran once the program is in memory the Virus can delete the file. It can corrupt files randomly. Some destructive viruses are not designed to destroy random data but instead randomly delete or corrupt files. It can cause write protect errors when executing .exe files from a write protected disk. Viruses may need to write themselves to files which are executed because of this if a diskette is write protected you may receive a write protection error.

It can convert .exe files to .com files. Viruses may use a separate file to run the program and rename the original file to another extension so the exe is ran before the com.

It can reboot the computer when a files is ran. Various computers may be designed to reboot the computer when ran.

WHAT VIRUSES MAY DO

The following are possibilities you may experience when you are infected with a virus. Remember that you also may be experiencing any of the following issues and not have a virus. Once the hard drive is infected any disk that is non-write protected disk that is accessed can be infected.

1. Deleted files 
2. Various messages in files or on programs. 
3. Changes volume label. 
4. Marks clusters as bad in the FAT. 
5. Randomly overwrites sectors on the hard disk. 
6. Replaces the MBR with own code. 
7. Create more then one partitions. 
8. Attempts to access the hard disk drive can result in error messages such as invalid drive specification. 

DETECTING VIRUSES

The most commonly used method of protecting against and detecting viruses is to purchase a third party application designed to scan for all types of viruses. A list of these protection programs are listed above.

Alternatively a user can look at various aspects of the computer and detect possible signs indicating a virus is on the computer. While this method can be used to determine some viruses it cannot clean or determine the exact virus you may or may not have.

 Conclusion

Computer viruses are perhaps the greatest threats to the computer. If not detected and promptly cured, computer virus attack could lead to the total breakdown of computer a installation. With the aid of our discussion in this unit, students should be able to prevent, detect and clean viruses in a computer installation.