Problem with virus

I have no idea what that is.

bash is a command-line interpreter (shell), and chsh is a command often used to select which shell you want to use as your default command-line interpreter (e.g., in Terminal). Neither should be continually popping up messages on your screen. As for NEARWOODCE – never heard of it.

If you go into Terminal and you see a message asking you to enter the command

chsh -s /bin/zsh

that message is probably just a "nag" from Apple, trying to get you to change your default shell to zsh, the one that they now prefer. But this nag wouldn't just pop up on your screen, out of the blue. You would need to run Terminal to see it.

I wonder if you're getting Web notifications from some scam site – notifications that are intentionally confusing; that the scammer hopes you will click on. You might want to skim

Stop unwanted Notifications - Apple Community

Please read About those "<app> will damage your computer" messages - Apple Community.

The nag message in that screenshot looks like the Apple one. The default shell on my current Mac is zsh, but if I run bash, I get

% bash

The default interactive shell is now zsh.
To update your account to use zsh, please run `chsh -s /bin/zsh`.
For more details, please visit https://support.apple.com/kb/HT208050.

I think there must be something in the bash system startup scripts that blindly prints this message without regard to what your default shell selection actually is.

Looks like something or someone tried to run the whole nag message as a command. The shell rejected the line starting with "The" (command not found), but picked up on the quoted chsh command and actually ran it. That command then asked you to show you had the right to change your default shell (by entering your password).

You can leave it as-is if you don't mind seeing the nag message.

The version of bash that Apple ships with macOS is very outdated, and might have security holes – but programs that run shell scripts have the option to specify which command-line interpreter to use. That would override the chsh selection.

That leaves the question of which shell you want to use when you go into Terminal. There are differences, and if you were very familiar with bash and zsh, you might have a preference for one or the other. It doesn't sound like that would be the case here.

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Other World Computing – Rocket Yard Blog – Moving From bash to zsh: Terminal changes in macOS Catalina

"Bash and Zsh have a very high level of compatibility between them. Both are based on the older Bourne shell. It’s likely most Bash commands and scripts you may be using will run just fine under the Zsh."

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