Blackhat SEO, or spam-seo, is a malicious technique used to manipulate the search engine results in order to benefit a website in terms of relevance. The payload is based on .htacess rules, thus intended for server-side use and the payload is executed directly on the server, before the site is rendered. Only the payload result (spam content, redirect) is visible in the browser, not the malicious code itself.
Any Apache based web server hosting vulnerable software or with compromised credentials.
Review your .htaccess rules and remove any RewriteRule that you do not recognize