Simplify the following text for a Grade 12 native English-speaking person.
Original: A zombie computer ( often shortened as zombie ) is a computer connected to the Internet that has been compromised by a cracker , computer virus or trojan horse and can be used to perform malicious tasks of one sort or another under remote direction .
Simplified: A zombie computer ( often shortened as zombie ) is a computer attached to the Internet that has been compromised by a hacker , a computer virus , or a trojan horse .