A computer virus is a software program which is able to replicate itself and spread from one infected computer to another. The infected objects can be system, program or document files. After infecting your computer, it might slow it down, damage the contents of the infected files, mislay the data or defect your computer systems normal operation.
The virus can also use your computer to propagate illegal adverts and send spam emails that exploit security (adWare), steal your personal information such as bank account number, credit card number etc. (SpyWare). Some types of viruses might use your computer to create a bot net (virtual computer network) to attack other server systems and websites etc.
There are a number of computer viruses that can impede the functioning of your computer. Here are some of the different types of viruses:
Trojan Horse: It is an email virus that is created by a file attached to the email. If opened, it may scour your hard drive for any personal and financial information such as your social security, account and PIN numbers. Once it has collected your info, it is sent via the internet to a hacker or thief.
Macro Virus: It is a computer virus that infects the Visual Basic language documents for applications such as Microsoft Word, Microsoft Excel etc. This type of virus can cause damage (such as removing data on the hard disk for example).
Worms: It is a program that has the ability to self-replicate itself. It can move from one computer to another and replicate itself in your computer system then spread hundreds of its copies to other computers that might cause wide spread damage.
Rootkit Virus: It is a program that is possible to cover the processes, files and data in the computer Registry (a database which is used to save Windows’s system and program settings). Rootkit is usually used to hide the activities of viruses and processes which harm your computer. It is to help a hacker to control the system.
Bootsector Virus: A virus which attaches itself to the first part of the hard disk that is read by the computer upon bootup. These are normally spread by floppy disks.
Polymorphic Virus: Polymorphic viruses encode themselves in a different way (using different algorithms and encryption keys) every time they infect a system. This makes it impossible for anti-viruses to find them using string or signature searches (for they are different in each encryption) and then it goes on creating a large number of copies.
Logic Bombs: It is a program that is used to send many data to the same email address and overwhelm the system or block the server connection. It is also used to threaten others (for example mail bomb etc.).
Memory Resident Virus: This type of virus dwells in the RAM. From there it can overcome and interrupt the operations executed by the system. It can corrupt files and programs that are opened, closed, copied, renamed etc.
Multipartite Virus: These viruses spread in multiple ways. It might vary in its action depending upon where it’s installed and the presence of certain files.
These are 3 common ways that your computer may get infected by viruses:
Email: You get an email from a person that contains one or more viruses. If the attachment is opened, the viruses may infect files in the computer. The viruses might also send emails to people from your email address book or email folders automatically. So, you should not open unknown attachments in emails or do a virus scanning after opening them.
Internet: If you download an exe file or a data file from the Internet or other shared networks, viruses might be transferred to your computer. Sometimes the free software programs on the Internet have viruses especially if downloading from sources such as Torrent or Usenet news groups. Therefore, if necessary, you should download files from trusted resources.
Peripheral devices: The devices such as MP3 player, USB thumb drive, Memory card or CD Rom are also means for spreading viruses. So, remember to do a virus scan for them after they are connected to your computer.
These are some of symptoms which may indicate virus activity: