Define what botnet is in one sentence.
A botnet is a network of malware-infected devices controlled by a hacker to perform tasks such as distributing spam messages, launching denial-of-service attacks, and stealing sensitive information.
Complete the following task based on the instruction and optional input provided.### Instruction:
Define what botnet is in one sentence.

### Output:
A botnet is a network of malware-infected devices controlled by a hacker to perform tasks such as distributing spam messages, launching denial-of-service attacks, and stealing sensitive information.