Computer virus Assignment help
A computer virus is malicious code that replicates by copying itself to another program, computer boot sector or document and changes how a computer works. A virus spreads between systems after some type of human intervention. Viruses replicate by creating their own files on an infected system, attaching themselves to a legitimate program, infecting a computer’s boot process or infecting user documents. The virus requires someone to knowingly or unknowingly spread the infection. In contrast, a computer worm doesn’t require human interaction to spread. Viruses and worms are two examples of malware which can include any variety of malicious code.
A virus can be spread by opening an email attachment, running an executable file on your device, visiting a website that’s infected with malware, or viewing website ads through malvertising. These are some ways that viruses can be spread. Once a virus has infected the host, it can infect other system software or resources, modify or disable core functions or applications, and copy, delete or encrypt data. Some viruses begin replicating as soon as they infect the host, while other viruses will lie dormant until a specific trigger causes malicious code to be executed by the device or system.
Many viruses have evasion capabilities designed to avoid being detected by antivirus software. Polymorphic viruses are more difficult to detect, since they constantly change their code every time they get new data.
Types of computer viruses
File infectors. Some file infector viruses attach themselves to program files, usually selected COM or EXE files. Others can infect any program for which execution is requested, including SYS, OVL, PRG and MNU files. When the infected program is loaded, the virus is loaded as well. Another type of virus is the file-infecting virus. They come as a whole program or single script you receive as an attachment to a mail.
Macro viruses. These viruses specifically target macro language commands in applications such as Microsoft Word and other programs. In Word, macros are saved sequences for commands or keystrokes that are embedded in the documents. Macro viruses, or scripting viruses, can add their malicious code to the legitimate macro sequences in a Word file. In recent versions of Microsoft Word, macros were turned off by default. There was a notable exception to this: Some hackers have been able to trick their targets into turning macros on and running a virus.
Overwrite viruses. Some viruses are designed specifically to destroy a file or application’s data. After infecting a system, an overwrite virus begins overwriting files with its own code. These viruses can target specific files or applications or systematically overwrite all files on an infected device. An overwrite virus can install new code in files and applications that programs them to spread the virus to additional files, applications and systems.
Polymorphic viruses. A polymorphic virus is a type of malware that has the ability to change or apply updates to its underlying code without changing its basic functions or features. This process helps a virus evade detection from many antimalware and threat detection products that rely on identifying signatures of malware; once a polymorphic virus’s signature is identified by a security product, the virus can then alter itself so it will no longer be detected using that signature.
Resident viruses. This type of virus embeds itself in the memory of a system. The original virus program isn’t needed to infect new files or applications. Even if the original virus is deleted, the version stored in memory can be activated when the operating system (OS) loads a specific application or service. Resident viruses are problematic because they can evade antivirus and antimalware software by hiding in the system’s random access memory (RAM).
Rootkit viruses. A rootkit virus is a type of malware that installs an unauthorized rootkit on an infected system, giving attackers full control of the system with the ability to fundamentally modify or disable functions and programs. Rootkit viruses were designed to bypass antivirus software, which typically scanned only applications and files. More recent versions of major antivirus and antimalware programs include rootkit scanning to identify and mitigate these types of viruses.
System or boot sector viruses. These viruses infect executable code found in certain system areas on a disk. They attach to the disk OS (DOS) boot sector on diskettes and USB thumb drives or the master boot record (MBR) on hard disks. In a typical attack scenario, the victim receives a storage device that contains a boot disk virus. When the victim’s OS is running, files on the external storage device can infect the system; rebooting the system will trigger the boot disk virus. An infected storage device connected to a computer can modify or even replace the existing boot code on the infected system so that, when the system is booted next, the virus will be loaded and run immediately as part of the MBR. Boot viruses are less common now as today’s devices rely less on physical storage media.
How does a computer virus spread?
The distinguishing characteristic of a virus is it spreads from system to system after a user takes some action that either intentionally or accidentally facilitates that spread. This spread is known as virus propagation, and there are many different techniques viruses can use to propagate between systems. The simplest example occurs when a virus is contained within an executable file that a user downloads from the internet, receives in an email message or copies from a removable storage device. As soon as the user executes that file, the virus springs into action, running malicious code that infects the user’s system.
Other viruses can spread through more complex mechanisms. In those cases, a virus running on an infected system may take action to begin its own propagation. For example, a virus might copy itself to all removable media installed on a system, attach itself to email messages sent to a user’s contacts or copy itself to shared file servers. In those cases, the lines become blurred between viruses, which require human assistance to spread, and worms, which spread on their own by exploiting vulnerabilities. The key difference is the virus will always require a human to take an action that enables that final step in the propagation process, while a worm does not require this human assistance.
Viruses can also spread between systems without ever writing data to disk, making them more difficult to detect with virus protection and virus removal mechanisms. Most fileless malware is activated when a user visits an infected website and then runs completely within the target system’s memory, carrying out their malicious payload and then disappearing without a trace.
How do computer viruses attack?
Virus propagation is only half the equation. Once a virus gains a foothold on a newly infected system, it begins to carry out whatever exploit the virus author designed it to perform. This is the payload delivery process, where the virus attacks the target system. Depending on the techniques the virus uses and the privileges of the user who created the infection, the virus may be able to take any action it desires on the target system. One of the main reasons security professionals advise organizations to avoid Privilege Elevation is that it amplifies the consequences of a security breach. It’s important to not grant access beyond what’s needed when managing these platforms.
A virus has many different payloads that you can encounter, but one of the most common is stealing data. Such a payload would breach the principles of cyber security by compromising confidentiality, integrity and availability. For example, a virus might search the local hard drive (HD) for Social Security numbers, credit card numbers and passwords, and then funnel those back to the attacker. Integrity attacks seek to make unauthorized modifications or deletions of information stored on the system. For example, a virus might delete files stored on a system or make unauthorized modifications to the OS to avoid detection. Availability attacks seek to deprive the legitimate user access to the system or the information it contains. For example, ransomware is a type of virus that encrypts information on the user’s HD, preventing legitimate access. It then demands the payment of a ransom in exchange for the decryption key.
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