Introduction
An Antivirus software is like a guard that identifies and destroys viruses on your system before the virus can cause any serious damage to the system such as deleting important files or formatting your system. AntiVirus software can also protect your system from harmful programs such as trojans and worms.
Types of Computer Viruses
The computer virus is a program written that can attaches itself to a file. When the infected file is opened, the infects other files on the system, and also spreads to other systems with the help of infected files. Viruses damage the system by deleting files on the system, increasing these files sizes, or automatically formatting the system.
Boot Viruses
The boot sector virus copies the virus code in the boot sector of the disk, this ensures that the virus is always executed and loaded into the memory when the system starts. Once in the memory, the virus infects other files and floppy disks inserted in the drive and spread it to other systems. For example, the virus Tequila infects all the EXE files on the system and also infects the master boot record of the hard disk.
Polymorphic Viruses
A person can keep on changing the way he looks to disguise himself this makes it difficult to trace a person. Similarly, polymorphic viruses are coded in such a way that they infect a system and change their signature before infecting the next system. Thus, the antivirus software finds it difficult to identify the virus, as it looks different after every infection. For example, the virus Hare copies the virus code in the boot sector of the hard disk and infects floppy disk inserted in the system, it also changes the virus's signature frequently to prevent antivirus software from detecting it.
Macro Viruses
Macros are blocks of code written to automate frequently performed tasks and embedded in a program file such as word document or an Excel worksheet. When a macro having the virus code is executed, it infects the files on the system. For example, the Love Bug virus erases files on the infected system and emails a copy of the macro virus to contact from the user's address book.
Worms
Worms are programs that replicate and spread to other systems. A worm resides in the system memory and spreads without attaching itself to a file. They may cause damage to the system such as deleting files from the system and may also the system may slow down. For example, the worm Melissa attaches itself to an email and sends the email to all the contact specified in the user's address book, it also clogs email servers.
Trojans
A Trojan is a program file that claims to do something but it actually does something that is not required. For example, a trojan may pose as a computer game but when it is executed it may also delete files from your system or email the passwords stored on your system to the Trojan writers email address. Trojans also allow remote users and hackers to gain unauthorized access to your system. The Trojan Subseven allows a hacker to take control of the mouse, eject this CD-ROM drive, and delete/download/upload files from the system. The Trojan Trojan. Treb supplies hackers system information and the system IP address.
Spywares
Spywares stores personal information and surfing habits of the user sends them to its website without informing the user. Many spyware gets installed as a free download while installing an application. It does not harm the computer as a virus does not but it used to get user information for monetary games. It may be a security threat, as it can gather personal information which may be used against you.
The following problems indicate that a spyware or other unwanted software installed on your computer:
- Unwanted advertisements pop-up even when not connected to the web
- Web browsers settings are changes automatically
- Unable to remove unwanted toolbar from the browser
- Computer performance slows down
- Computer crashes very frequently
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