Question

Discuss the five categories of viruses and state the way that you can fight viral attacks.

Answer 1

Virus:

A virus is a malicious program that is loaded in a user's computer without his/her knowledge. If the user executes the virus files, it replicates itself, affects other files on the system and sometimes makes the system behave in an unwanted way.

Five categories of viruses:

1. Boot virus:

This type of virus affects the hard disk by copying the master boot program to a different location of the hard disk. The master boot program is found in the first sector of the disk.

• Sometimes this virus even overwrites the boot sector program file.

• It makes the system startup difficult and messages such as "Invalid system disk" are often seen on the screen when the system is affected by the Boot sector virus.

• Once executed, it affects other floppy disks.

• One of the mediums they use to spread to other parts is DOS commands.

Michelangelo is an example of this virus.

2. Trojan Virus:

It is a type of virus that hides behind a legitimate-looking software.

• It tries to gain access to a computer by tricking the user to click on software.

• Once installed in your system it can delete, block, modify, and copy data.

• It disrupts the performance of the system and the network.

• It has many subsets such as data sending, remote access, FTP Trojans, DoS, etc.

• It does not self-replicate but can create a backdoor in your system allowing the malicious user to use your system.

Trojan-IM is an example of this virus.

3. Polymorphic virus:

This type of virus creates multiple copies to hide its identity. In all the different copies malicious code routine remains the same. What makes them undetectable is the different encryption keys used for different copies.

• It is also called the shape-shifting virus.

• For each copy, it alters the byte values of contents. This makes it hard for a virus detection program to detect it.

• The encryption of the contents doesn't let antivirus software identify it.

• They can have thousands of copies.

Bagle is an example of this virus.

4. File virus:

This type of virus injects malicious code into an executable file. In most cases, it affects files with .exe and .com extensions.

Once the file is accessed it is overwritten by the virus.

It can also spread over the network and affect other systems.

• Script virus is an example of a file virus. This type of virus is a subset of file virus and gets executed when you visit a malicious page.

• This page could have advertisements or some malicious code running in the back end. It usually enters your system from advertisements on the pages.

• Some clickable links also contain this virus.

• This type of virus can change your homepage on your web browser, slow down your system, etc.

• It causes the hackers to inject client-side code into the web page and steal the information of the visitor of the page such as cookies.

• If the attacker is able to hijack your session cookies using a script virus, your identity is impersonated by the attacker, exposing your data to them.

DDoS is an example of this virus.

5. Resident Virus:

This type of virus stores itself in the computer memory and affects other files. It starts spreading from one place to another. It can even affect the devices connected with the system.

• It doesn't require execution to infect other files.

• It only waits for the programs or files in the system to get activated.

• It is considered one of the worst kinds of viruses as it doesn't require execution.

• It can sometimes attach itself to the anti-virus program and affect all the files when the anti-virus is run to scan the files of the system.

• This type of virus runs whenever the Operating system loads.

CMJ is an example of this virus.

Ways to fight Virus Attacks:

1. Buy licensed software:

Buying an operating system from a licensed retailer can help you receive an upgrade in software to block the new viruses. It is also encouraged to buy registered anti-viruses.

2. Find a reputable antivirus software:

Sometimes a free anti-virus software is a virus program in disguise. Always prefer the licensed or registered software program.  

3. Keep your software up to date:

Stay up-to-date with any new advancements made in the software. You can subscribe to the website or retailer from where you bought the software. They can send you updates on when a new version or plug-ins are released.

4. Pop-up blocker:

Many browsers such as Google Chrome, Firefox, etc. use pop-up blockers. These are used to keep dangerous ads from showing on your system screen.

5. Avoid clicking on unknown links:

Do not click on the attachments or links you receive in your email when the sender of the email is not known. Fraudulent emails are the number one source of viruses. No matter how genuine or friendly someone appears, delete the mails from unfamiliar companies or persons.

6. Avoid clicking or visiting unknown sites:

Whenever you are routed from one to another website without your consent, close the site.

When you visit a site, it is advised not to click on anything especially the advertisements.

7. Have back up:

It is also encouraged to have period back up to a remote or external storage device. Having data backed up ensures that if your data is affected by malicious code, you still have the original data intact.