Is CryptoLocker a virus?

Could you please elaborate on the nature of CryptoLocker and whether it constitutes a virus? I've heard some concerning whispers about this software, and I'm interested in understanding its true impact. Specifically, does CryptoLocker exhibit malicious behavior such as encrypting files without the user's consent and demanding a ransom for decryption? Additionally, how widespread is this threat, and what measures should users take to protect their systems from such attacks? I'd appreciate a concise yet thorough explanation to help me understand the gravity of this issue.