The infection is aimed at websites built on the popular WordPress CMS. It is targeting sites with outdated (vulnerable) plugins or weak admin passwords. Malware is highly obfuscated and attempts to inject SPAM to the hacked website. The infector PHP code is buggy and corrupting legitimate website files. The only known solution (after removal of injected malware) is restoring these corrupted files from a clean backup. If you suspect you have been impacted by this infection rest assured that our team is ready and actively cleaning this mess up.”]
Source: https://blog.sucuri.net/2014/07/malware-infection-breaking-wordpress-sites.html