Ask yourself how they would know if you had a virus? When they say that you have a "trojan virus", that you have some huge number of viruses, or that "your iCloud is being hacked!!!", that's a classic scam. They'd love it if they knew enough about your bank account to reach out and clean it out without your help, but they don't, so they are resorting to these "phishing" tactics to scam you.