Stealth viruses are computer viruses that are specifically designed to hide their presence on an infected system. They are known for their ability to camouflage themselves and avoid detection by antivirus software. These viruses often infect the boot sector of a computer's hard drive, which allows them to take control of the system as soon as it boots up.

Here is a detailed explanation of each of the given options:

a) Trojan: Trojans are a type of malicious software that disguise themselves as legitimate programs or files. Unlike stealth viruses, Trojans do not typically infect the boot sector or delete data upon system boot. Instead, they often perform actions such as stealing personal information, installing additional malware, or providing unauthorized access to the infected computer.

b) System infectors: System infectors are viruses that infect executable files on a system, including both program files and system files. While these viruses can cause damage to the infected files, they do not necessarily hijack the system upon booting or delete data.

c) Stealth virus: As mentioned earlier, stealth viruses are designed to hide their presence on an infected system. They often infect the boot sector of a computer's hard drive, allowing them to gain control of the system as soon as it boots up. Some stealth viruses may also delete or corrupt data on the system, depending on their specific payload.

d) Boot infectors: Boot infectors, also known as boot sector viruses, infect the boot sector of a computer's hard drive or other bootable media. These viruses alter the boot process, allowing them to execute their code before the operating system loads. While boot infectors can cause various types of damage, including data deletion, not all boot infectors necessarily delete data.

Therefore, the correct answer to the question is option 'C' - Stealth virus. Stealth viruses are designed to hijack the system upon booting and have the capability to delete data.