Viruses Explained PDF

**VIRUSES** 1**[. Boot Sector Virus]** \- This type of virus infects the master boot record and it is challenging and a complex task to remove this virus and often requires the system to be formatted. Mostly it spreads through removable media. 2\. **[Direct Action Virus]** \- This is also called...

**VIRUSES** 1**[. Boot Sector Virus]** \- This type of virus infects the master boot record and it is challenging and a complex task to remove this virus and often requires the system to be formatted. Mostly it spreads through removable media. 2\. **[Direct Action Virus]** \- This is also called non-resident virus, it gets installed or stays hidden in the computer memory. It stays attached to the specific type of files that it infect. It does not affect the user experience and system's performance. 3\. **[Resident Virus]** \- Unlike direct action viruses, resident viruses get installed on the computer. It is difficult to identify the virus and it is even difficult to remove a resident virus. 4\. **[Multipartite Virus]** \- This type of virus spreads through multiple ways. It infects both the boot sector and executable files at the same time. 5\. **[Polymorphic Virus]** \- This type of viruses are difficult to identify with a traditional anti-virus program. This is because the polymorphic viruses alters its signature pattern whenever it replicates 6\. **[Overwrite Virus]** \- This type of virus deletes all the files that it infects. The only possible mechanism to remove is to delete the infected files and the end-user has to lose all the contents in it. Identifying the overwrite virus is difficult as it spreads through emails. 7\. **[Space filler Virus]** \- This is also called "Cavity Viruses". This is called so as they fill up the empty spaces between the code and hence does not cause any damage to the file. 8\. **[File Infector Virus]** \- Attached with program files, such as.com or.exe files. Some file infector viruses infect any program for which execution is requested, including.sys,.ovl,.prg, and.mnu files. Consequently, when the particular program is loaded, the virus is also loaded \- Besides these, the other file infector viruses come as a completely included program or script sent in email attachments. 9\. **[Macro Virus ]** \- As the name suggests, the macro viruses particularly target macro language commands in applications like Microsoft Word. The same is implied on other programs too. In MS Word, the macros are keystrokes that are embedded in the documents or saved sequences for commands. The macro viruses are designed to add their malicious code to the genuine macro sequences in a Word file. However, as the years went by, Microsoft Word witnessed disabling of macros by default in more recent versions. Thus, the cybercriminals started to use social engineering schemes to target users. In the process, they trick the user and enable macros to launch the virus. 10\. **[Rootkit Virus]** \- The rootkit virus is a malware type which secretly installs an illegal rootkit on an infected system. This opens the door for attackers and gives them full control of the system. The attacker will be able to fundamentally modify or disable functions and programs. Like other sophisticated viruses, the rootkit virus is also created to bypass antivirus software. The latest versions of major antivirus and antimalware programs include rootkit scanning. 11\. **[System or Boot-record Infectors ]** \- Also known as Boot sector virus. The Boot-record Infectors infect executable code found in specific system areas on a disk. As the name implies, they attach to the USB thumb drives and DOS boot sector on diskettes or the Master Boot Record on hard disks. Boot viruses are no more common these days as the latest devices rely less on physical storage media. 12\. **[Browser Hijacker]** \- This type of virus infects your web browser in which it will bring you to different websites. Typically, if you key in a domain name in the internet address bar, the browser hijacker will open multiple fake websites that may harm your computer. On the other hand, most trusted browsers have built-in features to block them ahead. 13\. **[Web Scripting Virus]** \- This virus lives in certain links, ads, image placement, videos, and layout of a website. These may carry malicious codes in which when you click, the viruses will be automatically downloaded or will direct you to malicious websites. 14\. **[Directory Virus]** \- Directory viruses change file paths. When you run programs and software that are infected with directory viruses, the virus program also runs in the background. Further, it may be difficult for you to locate the original app or software once infected with directory viruses. 15\. **[Encrypted Virus]** \- This type of virus uses encrypted malicious codes which make antivirus software hard to detect them. They can only be detected when they decrypt themselves during replication. Although they don't delete files or folders, they can badly affect PC performance. 16\. **[Network Virus]** \- Basically, this type of virus spreads out through Local Network Area (LAN) and through the internet. These viruses replicate through shared resources, including drives and folders. When network viruses enter a computer, they look for their potential prey. Dangerous network viruses include [Nimda and SQLSlammer.] 17\. **[Companion Virus]** \- This is a type of virus that doesn't survive without accompanying an existing file or folder. In order to carry out damages, the file or folder being accompanied by companion viruses should be opened or run. Some examples of companion viruses include Terrax.1069, Stator, and Asimov.1539. 18\. **[Nonresident Virus]** \- Nonresident viruses replicate through modules. When the module is executed, it will select one or more files to infect. 19\. **[Stealth Virus]** \- Stealth viruses trick antivirus software by appearing like they are real files or programs and by intercepting its requests to the OS. Some antivirus software cannot detect them. Sometimes, it temporarily removes itself from the system without deletion. 20\. **[Sparse Infector]** \- Sparse infectors use different techniques to minimize its detection. They are viruses that infect "occasionally". For example, they may only want to infect a program every tenth execution. Because they are occasional infectors, antivirus software has a hard time detecting them.