PHP malware is one of the most common malicious code found on the internet, mostly because it is the leading server-side language used on websites, followed by ASP, Java, ColdFusion and Perl (source).
In order to address this issue, our tools are capable of detecting and cleaning up malware that weren't collected yet, but meet a complex set of characteristics that are considered malicious.
This malicious code affects any vulnerable or compromised website that is configured to interpret the script language.
Inspect your site's files, specially theme related, to find for code you don't recognize. Look for any encoded or obfuscated PHP code.
Also, you can sign up with us and let our team remove the malware for you.