How can I know if my iPhone has viruses or is hacked?

Unless you have jailbroken your phone, you have NOT been hacked. What you got was a Phishing Scam message, designed to scare you into providing personal details or buy something you absolutely do not need.

Never respond to a scam email or text.

See this for more information --> Recognize and avoid phishing messages, phony support calls, and other scams - Apple Support

If running iOS 13 or earlier versions, check: Settings - Passwords & Accounts - Accounts - Any rogue entries here? If so, delete the rogue account. 

If running iOS 14, check: Settings - Calendar - Accounts - Any rogue entries here? If so, delete the rogue account. 

The Apple support article is below. 

Remove calendar spam

Video support

Read this thread. Unless you have jailbroken your phone you have NOT been hacked.

No.

And why would a hacker even tell you that? If they could really hack in, they'd keep it a secret as long as they could until they had cleaned out your bank accounts and made as many charges against your credit as possible.

I received a message last night that my phone is being hacked. Is it possible?

I have gotten a virus that has attacked my calendar

How to know if my iPhone is hacked?

Is it possible to download malware or any other kind of virus by downloading a picture from a text message?

An image is just an image. It has no code to run.

jbubbs wrote:

Is it possible to download malware or any other kind of virus by downloading a picture from a text message?

No.

It says u have 13 viruses on ur iPhone I’m really worried please help me

Did you read any of the responses above?