Could a virus reset my passcode?

If your phone wasn't jailbroken it wasn't a virus. You cannot reset the phone's passcode, but you can restore iOS by following these instructions-->If you forgot the passcode for your iPhone, iPad, or iPod touch, or your device is disabled - Apple Support

If you mean your Apple ID password it's possible that your Apple ID was hacked. Post back if that's what you meant and we can deal with that.

No, you are wrong. Those are the instructions to reset your phone to factory conditions, which also resets the passcode. If it asks you to enter a passcode you are not following the instructions correctly.

If you follow the instructions exactly you would not be locked out at all. The restore resets the passcode to none.

Forget Passcode or Restore Device

1. If you forgot the passcode for your iPhone, iPad, or iPod touch, or your device is disabled
2. How to erase your iOS device & then set it up as a new device or restore it from backups

For help with the above or later models including iPhone 7, 7s, 8 or later, iPad Pro 11" and iPad Pro 12.9" models please refer to If your iPhone, iPad, or iPod touch won't turn on or is frozen.

If the above doesn’t work for you, then:

Follow these steps to place your iOS device into recovery mode: iPhone DFU mode explained, and how to enter DFU mode on your device.

If all fails then make an appointment at the Apple Genius Bar for service. If you need to find an Apple Store - Find a Store - Apple. If you did not purchase it from Apple then you will need to look to the vendor for service.