They include commercial WordPress themes and plugins. They are the web equivalent of pirated software. Nulled scripts are commercial web applications that you can obtain from pirate websites that have been modified to work without a license key. I’ve summarized the details and our response: Our friends over at Fox-IT based in Delft in the Netherlands just contacted me with some amazing research they’ve just published. If you’re technically minded and want as much detail as possible, I recommend you skip this blog entry and head straight over to the Whitepaper that Fox-IT has published on the CryptoPHP backdoor (It’s 50 pages). WordPress Security: Nulled Scripts and the CryptoPHP Infection
