2015 MacBookPro 13 - Catalina 10.15.1. Updates?

The only full installer Apple makes available for Catalina is 10.5.7

Use the App Store

To download macOS from the App Store, use a Mac that is compatible with that macOS. If your Mac isn't compatible, the App Store dims the Get button, says that the macOS is not compatible with this device, or says that the requested version of macOS is not available.

If these links don't work as expected, try again using Safari, which is in your Applications folder.

Sonoma 14

Ventura 13

Monterey 12

Big Sur 11

Catalina 10.15

Mojave 10.14

High Sierra 10.13

1. Use these links to find macOS in the App Store.
2. Cick the Get button in the App Store to begin downloading. Software Update might open and ask you to download from there.
3. After downloading to your Applications folder, the installer opens automatically. Follow the onscreen installation instructions. Or quit without installing to leave the installer in your Applications folder for later use.

How to download and install macOS - Apple Support

Very unlikely you have a Virus, just likely to be an annoying popup.

macOS Sierra 10.12 - macOS Monterey 12.x, Malewarebytes v4.12.0

https://www.malwarebytes.com/mac

https://support.malwarebytes.com/hc/en-us/articles/360038524394-Malwarebytes-home-products-and-macOS-compatibility

Since you are currently running macOS Catalina 10.15.1, you should use the System Preferences > Software Update to download the latest updates - not upgrade - for Catalina. The latest will put the machine at 10.15.7.

If System Update only seems to provide a link to a newer OS, then skip that and go straight to the macOS Catalina 10.15.7 Combo Update located here.

Download the combo updater and apply that to your MacBook Pro. It will include all of the latest revisions available for Catalina.