Force Byte
Computer Virus - Introduction and Prevention (2)

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I introduced the first four common computer viruses last time. Hence you think that your computer is easily attacked by computer viruses, don't you? But please don't worry. As I mentioned in the last issue, the computer virus prevention and support team of ITB is always standing behind you. They have already installed the most updated anti-virus software to your desktop computers. So if you could make an extra effort NOT to browse suspicious websites, open e-mails from unknown sources, download and execute files recklessly, and at the same time keep track of the latest information on computer viruses and take appropriate precautions, there will be little chance that your computers will be infected by them.

Let me continue with the remaining four types of common computer virus:

Type	Infection Channel
5. Stealth Virus	Like the file infector virus, it will attach itself to target executable files. However, since it also resides in the main memory and interfere with the system operation, you will not realise any size differences for the infected files or main memory when you check them with the "DIR" or "MEM" commands. So the virus goes unnoticed.
6. Polymorphic/Mutation Virus	This virus is so destructive that when it infects a programme file, it mutates and replicates the new virus code into the programme file. In that case, the anti-virus software cannot detect its existence and it can keep multiplying.
7. Trojan Horse	It is named after "Troy", the city in Greek mythology. The virus does not cause damage to the computer immediately or directly after it has gained access to the system. However, the hacker is able to hack your computer to steal your data and even control it through web. In view of this, strictly speaking, it should be classified as "computer worm" instead of virus.
8. Web Virus	Basically, it differs not much from other types of viruses except that it attacks through web. Once it has invaded into your computer, it will send itself out massively in the form of email attachments to any contacts in the address book of applications like "Outlook". Sooner or later, it will spread to every corner of the world and keep all servers so busy that they cannot accept any service requests. Apart from causing email flooding, it will attack files with extensions such as .JPG, .MP3, .TXT, etc. The once notorious "I LOVE YOU" virus is a typical example, which will send out a large number of emails and attack files to cause damage to the infected computers.

Now you have a clearer picture that some computer viruses can hide and change themselves to evade the detection of anti-virus software. Some may even become tools for hackers to steal important data or maliciously take control of your computer to attack other computers. Hence, you should always try your best to know how viruses attack and damage your computer, and then you can keep a closer watch and guard against them. The same old advice is: do not open the email attachments casually and do not download unknown software.

Last but not least, computer viruses can not only affect you and me, but will also threaten the global network security. Never take them lightly.

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(Email address: 'ITB_ForceByte_Editor@police.gov.hk')