An anonymous reader writes "ESET researchers, together with web security firm Sucuri, have been analyzing a new threat affecting Apache webservers. The threat is a highly advanced and stealthy backdoor being used to drive traffic to malicious websites carrying Blackhole exploit packs. Researchers have named the backdoor Linux/Cdorked.A, and it is the most sophisticated Apache backdoor seen so far. The Linux/Cdorked.A backdoor does not leave traces on the hard-disk other than a modified 'httpd' file, the daemon (or service) used by Apache. All information related to the backdoor is stored in shared memory on the server, making detection difficult and hampering analysis."