There is no specific number of YouTube ads you can click before encountering a virus. The risk is not determined by the quantity of clicks, but rather by the nature of the ad itself. While YouTube and Google have extensive systems in place to review and filter out malicious ads, some can still slip through.

Here's a breakdown of the risks and how to protect yourself:

The Danger of Malicious Ads (Malvertising)
Malvertising is the practice of using legitimate advertising networks to deliver malware or other malicious software. When you click on a malicious ad, it can redirect you to a website that attempts to infect your device.

Exploiting Browser Vulnerabilities: In the past, malicious ads sometimes exploited security vulnerabilities in web browsers or plugins like Java and Flash. These "drive-by downloads" could install malware without any further action from the user. Modern browsers and operating systems are much more secure, making this type of attack rare, but not impossible.

Phishing and Scams: More commonly, malicious ads lead to phishing sites that are designed to look like legitimate websites. The goal is to trick you into entering personal information, such as passwords or credit card numbers.

Adware: Clicking on a malicious ad can also lead to the installation of adware, which bombards you with unwanted pop-ups and ads, slows down your computer, and can change your browser's homepage.

How to Stay Safe
While you can't guarantee that every ad is safe, you can significantly reduce your risk by following these best practices:

Be Skeptical of "Too Good to Be True" Offers: If an ad promises an unbelievable discount, a free product, or a get-rich-quick scheme, it's likely a scam.

Verify Before You Click: If an ad for a product or service interests you, do not click the ad directly. Instead, open a new tab and navigate to the company's official website yourself. This bypasses any potentially malicious redirects.

Keep Your Software Updated: Regularly update your operating system, web browser, and antivirus software. These updates often include critical security patches that protect against new threats.

Use Ad Blockers: While using an ad blocker may violate YouTube's terms of service, many users choose to use them as a first line of defense against malicious ads and other online threats.

Enable Browser Security Features: Most modern web browsers have built-in security features that can warn you about suspicious websites or prevent them from loading. Ensure these features are enabled.

Install Antivirus/Anti-Malware Software: A reputable antivirus program can detect and block malware before it can infect your device, even if you accidentally click a malicious link.