I understand your concern about the "Trojan virus" pop-up you encountered on your iPhone. Unfortunately, you fell victim to a common scam designed to trick users into installing unnecessary and potentially harmful software. Since you installed the suggested app, you should take immediate action. First, delete the app you installed. Then, go to Settings > General > VPN & Device Management to check for and remove any suspicious profiles. Next, run a legitimate security scan using the free Malwarebytes app from the App Store. It's also wise to change passwords for important accounts (banking, email, etc.) from a different device if possible, enable two-factor authentication, and monitor your accounts for suspicious activity. In the future, remember that legitimate virus warnings don't appear as pop-ups in browsers, and Apple will never direct you to install third-party apps for security issues. If you're still concerned, you can back up your important data and perform a factory reset, or visit an Apple Store for professional assistance.