The correct answer is: A. Virus attack.
A Trojan horse is a type of malware that disguises itself as a legitimate program in order to trick users into installing it on their computers. Once installed, a Trojan horse can steal personal information, damage files, or even take control of the computer.
A virus is a type of malware that can replicate itself and spread from one computer to another. Viruses can damage files, steal data, or even take control of a computer.
A service attack is an attack that targets a specific service, such as a web server or email server. Service attacks can be used to disrupt service, steal data, or even take control of the service.
A Slammer worm is a type of malware that spreads rapidly from computer to computer by exploiting a vulnerability in the Microsoft SQL Server database software. Slammer worms can cause widespread disruption of computer networks.
A Melissa worm is a type of malware that spreads through email messages. Melissa worms can damage files, steal data, or even take control of a computer.
In conclusion, a Trojan horse is a type of malware that disguises itself as a legitimate program in order to trick users into installing it on their computers. Once installed, a Trojan horse can steal personal information, damage files, or even take control of the computer.