Trojan built to disable cloud antivirus

Crafty Chinese malware writers.

Microsoft has discovered a Trojan that aims to sever the connection between a device and the cloud antivirus (AV) service that is meant to protect it.

The Bohu Trojan, which targets Windows machines, contains three main functions: evade detection, install a filter that blocks traffic between the device and service provider, and prevent the local installation from uploading data to the server.

The attack appears to aim to knock out the additional layer of security that many antivirus companies have added to bolster defences and reduce the processing burden of ever-expanding signature databases.

"Cloud-based virus detection generally works by client sending important threat data to the server for backend analysis, and subsequently acquiring further detection and removal instruction," Jingli Li and Zhitao Zhou of Microsoft Malware Protection Center wrote on the company's blog.

"The process can take seconds to minutes, and is designed to remove malware not handled by the traditional on-the-box signature approach."

Kaspersky, Microsoft and Sophos have developed signatures for the Bohu trojan, which the researchers noted relies on the user installing, installing a rigged video codec.

According to Microsoft's researchers, the network driver that Bohu installs probes for HTTP request keywords and the cloud-server names of major Chinese AV vendors, Kingsoft, Qihoo, and Rising, the company involved in a corruption fiasco, which resulted in a suspended death sentence for a senior Chinese bureaucrat.