Complex sentence: Botnets sometimes compromise computers whose security defenses have been breached such as compromised devices, known as a "bot network virus", is created when a computer is penetrated by software from a "malware" (malicious software) distribution.
Split into simpler sentences: Botnets sometimes compromise computers whose security defenses have been breached. Each such compromised device, known as a "bot network virus", is created when a computer is penetrated by software from a "malware" (malicious software) distribution.