A resident virus works by embedding itself into a computer's memory, allowing it to infect files whenever they are executed.
Here's a breakdown of how it operates:
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Infection Phase:
- Entry: The virus typically enters the system through infected files (e.g., downloaded software, email attachments) or infected media (e.g., USB drives).
- Memory Residency: Once executed, the virus doesn't just run and disappear. Instead, it copies itself into the computer's Random Access Memory (RAM). This makes it "resident" – it's actively present in the system's core operations.
- Hiding: Some resident viruses employ stealth techniques to avoid detection. They might conceal their presence in memory or disguise themselves as legitimate system processes.
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Infection Mechanism:
- File Infection: While resident in memory, the virus monitors file execution. Whenever a program is run, the virus intercepts the process.
- Attachment: The virus then attaches a copy of itself to the executable file (e.g., .exe, .com). The next time the infected file is run, the virus is activated again, perpetuating the infection.
- Targeting: Depending on its programming, a resident virus might target specific types of files or applications. Some even attempt to infect antivirus software, compromising the system's defenses.
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Key Characteristics:
- Memory Resident: This is the defining characteristic. Unlike non-resident viruses that execute only when their host file is run, resident viruses stay active in memory.
- Fast Infection: Because they're already in memory, resident viruses can infect other files quickly.
- Difficult Removal: Their constant presence in memory makes them more challenging to remove than non-resident viruses. Specialized antivirus tools and techniques are often required.
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Types of Resident Viruses:
- Fast Infectors: These viruses focus on quickly infecting as many files as possible.
- Slow Infectors: These viruses infect files intermittently or after a certain period, making them harder to detect initially. They may also alter file modification dates to conceal their activity.
In essence, a resident virus establishes a persistent presence in a computer's memory, enabling it to spread rapidly and persistently by infecting files as they are executed, making them a significant threat to system security.
