CryptoPHP is a malicious script that provides remote attackers with the ability to execute rogue code on Web servers and to inject malicious content into websites that are hosted on them. According to Dutch security firm Fox-IT, which published a report about the threat last week, the backdoor is used primarily for black hat search engine optimization (BHSEO), an operation that involves injecting rogue keywords and pages into compromised sites to hijack their search engine rankings and push malicious content higher up in search results.