How to make a search result page as a 404 when there are no results?

hello.

I’ve been suffering from a massive internal site search spam attack on my site for about a year now.

They use wordpress’s search function /?s= or /search/ to link to malicious keywords and get them indexed by bots.

example.com/?s=k%EC%86%8C%EB%9D%BC%EB%84%B7%E2%86%97%20NAJA9. com%20%E2%95%84%EC%9A%B8%EC%A7%84%20%EB%A6%BD%EC%B9%B4%ED%8E%98%E3%8E%A2%EC%95%84%EC%82%B0%20%ED%9C%B4%EA%B2%8C%ED%84%B8%E2%96%A6%EB%8F%99%EB%8C%80%EB%AC%B8%20SM%EC%9B%90%EC%B8%84%E2%87%94%EC%9E%A0%EC%8B%A4%20%EC%97%AC%ED%96%89%ED%8C%8C%ED%8A%B8%EB%84%88%E2%94%8E%EC%9C%84%EB%A1%80%20%EC%95%84%EC%A3%BC%EB%A7%88%EB%A7%8C%EB%82%A8%E2%95%83

The Blocksy theme currently shows an HTTP response code of 200 when there are no search results, is there any way to change this to 404?

I would like to change it to 404 when there are no matching search results and 200 when there are.

Thanks.