This site was injected with some malicious code where in google search users can see adult sites' articles and when a user clicked on that link it redirects to other sites. As a result, Google also marked this site as infected with the virus.
I scanned all the files carefully and came to know the core WordPress files were infected. I have to clean up all the malicious code manually and submit the request to Google to recrawl.
Now the site is working perfectly fine with no issues.
