Yes, a factory reset will remove almost all viruses, as it erases all data and restores your phone to its original state. However, if the virus is in the phone’s firmware (rare), you may need to flash the stock ROM (Android) or contact Apple Support (iPhone).
Yes, some malware is designed to steal passwords, bank details, contacts, and other personal information. That’s why it’s crucial to disconnect from the internet as soon as you suspect a virus, and use strong, unique passwords for all your accounts.
Pop-ups may still appear if the virus left behind cached files or if you have a malicious browser extension. Clear your browser cache and history, and remove any untrusted extensions (Settings > Browser > Extensions).