What type of virus is designed to avoid detection by antivirus software?

A stealth virus is specifically designed to evade detection by antivirus programs. It does this by employing various techniques to hide its presence on the infected system. For instance, a stealth virus may modify the way data is reported to the operating system or to antivirus software, making it appear as though the infected files are not actually compromised. By intercepting system calls and altering the data returned, it can mask its actions, thus allowing it to operate without triggering alerts from security software.

In contrast, other types of viruses have different characteristics. Ransom viruses focus on encrypting files to extort ransom from users but do not emphasize evasion techniques against security measures. Boot sector viruses infect the boot sector of storage devices to execute early in the boot process, and while they can cause significant harm, they do not inherently incorporate stealth techniques to hide from antivirus detection. Macro viruses typically exploit software applications that use macros (like those in Microsoft Office) to spread, but they also lack the sophisticated evasion methods characteristic of stealth viruses.