Last week the Gumblar malware was neutralized when the files containing its malware infection code were replaced with code that attempted to neutralize iframes. Today, those files have been modified to redirect users to files on other websites that contain the malware code. Like the original websites that hosted the malware code, these new hosts are websites that have been compromised by the malware. This is different than most attacks where the malware code is stored on a website controlled by the individuals behind the malware.
The Gumblar malware, which returned in the past several weeks, appears to be neutralized for the moment. In its return, Gumblar was using compromised websites to host its malware code instead of a website owned by the person(s) behind the hack. Other websites that have been compromised by Gumblar, then have code inserted into them that causes a file, with the malware code, to be loaded from one the websites that host the malware.
Gumblar inserted backdoor scripts as part of its hack, which someone other than the original hacker could have used to change the code stored on the host websites. It is also possible that the originally hacker made the change for some unknown reason.