System Files Reference Book

File – a storage unit filled with data, information, settings, or commands about a program

The computer system consists of various files that use different amounts of its resources. Each PC system contains thousands of files located in different directories.

You can identify these files by their extensions (short additions at the end of their names). Regardless of the OS installed on your computer, files are organized with the help of folders. They are stored on a hard drive and other storage devices. Most of your files can be changed or renamed.

The most popular types of files are:

• System files
• Program files
• Data files
• Executable files
• Text files
• Directory files

Dangerous files pose a serious risk to the system

There are two groups of files: harmless and malicious. Harmless files are reliable system components necessary for proper PC functionality. They are associated with legitimate applications and should not be removed. The most important ones are system files, which are critical to the normal operation of a computer. Deleting or modifying such files can cause serious damage.

On the other hand, malicious files can severely harm your computer. They can significantly decrease system speed, stability, and functionality by consuming large amounts of memory and disk space. Detecting malicious files without security software is challenging because malware creators use various techniques to hide them in the system.

Main signs showing that a file is malicious

While it is not recommended to manually check a file's trustworthiness, as malicious files often have names almost identical to legitimate ones, several signs should prompt you to initiate a full system scan with an anti-virus tool.

• Spelling Mistakes: Malicious files may have subtle spelling errors in their names.
• Incorrect Location: Check the file's location. If a supposed system file is in C:\Program Files, it is likely malicious.

The easiest way to know whether your PC system is filled with malicious files is to scan it with reliable anti-malware.

Types of malicious files used in cyberattacks

Malicious files come in various forms and are used in different types of cyberattacks. Here are some common types:

• Executable files (.exe): These files can install malware directly onto a system when executed. They are often disguised as legitimate software.
• Dynamic link libraries (.dll): DLL files can be injected into running processes to execute malicious code.
• Script files (.js, .vbs, .bat): These files contain scripts that can automate tasks on the system. Malicious scripts can be used to download other malware or to exploit vulnerabilities.
• Document files (.doc, .pdf): These files can contain embedded malicious macros or scripts that execute when the document is opened.
• Compressed files (.zip, .rar): These files can be used to compress and hide multiple malicious files. When decompressed, the contained malware is executed.
• Temporary files (.tmp): Malware can use temporary files to store data or execute code without being detected easily.
• Link files (.lnk): These files can be used to trick users into executing malware by appearing as shortcuts to legitimate applications.
• Configuration files (.cfg, .ini): These files can be altered to change the behavior of legitimate applications to execute malicious actions.

Implementation of malicious files

Malicious files are implemented using various techniques to evade detection and infect systems:

• Phishing emails
  Attackers send emails with malicious attachments or links to download malware.
• Drive-by downloads
  Visiting compromised or malicious websites can result in the automatic downloading of malware.
• Social engineering
  Attackers trick users into executing malicious files by disguising them as legitimate software or updates.
• Software exploits
  Malware exploits vulnerabilities in software to execute malicious code.
• Fileless malware
  Instead of being stored on the disk, the malware resides in the system's memory, making it harder to detect.

Helping you identify malicious and legitimate files

For your convenience, we have created the Files section. Here, you can find hundreds of different files related to either legitimate applications or computer viruses. They can all be identified by their extensions. The most popular ones include .exe, .dll, .db, and .lnk. This section primarily focuses on malicious files to help you identify an infected PC system.

Each file's description includes a list of tools recommended for computer diagnosis. If you find that you are dealing with a malicious file, you should select one of our recommended programs to remove it from your computer.