Describe at least three kinds of security threats and how to protect against them.

1. Malware: This is a type of software designed to gain unauthorized access or cause damage to a computer. It includes viruses, worms, trojans, ransomware, and spyware. To protect against malware, it's important to install and regularly update antivirus software. It's also crucial to avoid clicking on suspicious links or downloading files from untrusted sources.

2. Phishing: This is a type of online scam where criminals impersonate legitimate organizations to steal sensitive data like credit card numbers and login credentials. To protect against phishing, it's important to be cautious of emails or messages that ask for personal information, especially if they instill a sense of urgency. Also, always double-check the email address of the sender and the URL of the website the email links to.

3. Denial-of-Service (DoS) Attacks: In a DoS attack, the attacker floods a network or server with traffic to make it unavailable to its intended users. To protect against DoS attacks, it's important to have a robust network infrastructure with redundancy and failover capabilities. Also, consider using DoS protection services that can detect and filter out DoS traffic.

Remember, the best defense against these and other security threats is a combination of strong, updated security software, a well-educated user base, and a robust network infrastructure.