It occurs to me that malicious code that scans WordPress etc. sites for vulnerabilities, installs itself, and sends spam and propagates itself does match the ge

It occurs to me that malicious code that scans WordPress etc. sites for vulnerabilities, installs itself, and sends spam and propagates itself does match the general shape of a virus (even to the point where pattern-matching antivirus would genuinely be effective against it). We just for whatever reason tend not to refer to it as a "WordPress virus," but rather e.g. a "reverse shell" or a "botnet."