The ZeroAccess rootkit used to be a problematic kernel-mode family of malware that was hard to remove; new versions of the malware itself have dropped the kernel-mode aspects. Now it operates entirely in user-mode memory. This shift in development has led Sophos researchers to dig deeper, and they found some interesting things.
ZeroAccess it an information stealing rootkit, which targets financial and personal information, but it has been tied to click-fraud, as well as other attacks such as DDoS. It can also be used as a delivery system, as infected hosts can be commanded to download addition malware to the system. Like most rootkits, ZeroAccess creates a botnet. So when the command servers are able to establish communications, the host is under the attacker’s complete control.
In June, when the changes to ZeroAccess were first detected, Sophos said that they user-mode memory changes were being aggressively distributed through the normal channels, including drive-by downloads, KeyGens, fake game downloads, and the like. In fact, the unified development changes were do widely distributed that “new samples of the old variant have all but dried up,” Sophos wrote.
In July, a report from Kindsight Security singled out ZeroAccess as a concerning threat, noting that it grew to over 1.2 million nodes over the second quarter.
"In recent months, we've seen the ZeroAccess botnet update its command and control protocol and grow to infect more computers while connecting to over one million computers globally," Kevin McNamee, security architect and director of Kindsight Security Labs, said in a statement this past July.
According to Sophos’ latest research, ZeroAccess has been installed more than 9 million times as of August 30, and retains more than 1 million actively infected systems under its control. These figures match the report from Kindsight, meaning that ZeroAccess is a persistent problem for enterprise networks, where it is commonly found. “ZeroAccess is a hugely widespread malware threat that has plagued individuals and enterprises for years. It has evolved over time to cater for new architectures and new versions of Windows,” Sophos explained in a blog post.
“Our research has discovered that the ZeroAccess botnet is currently being used for two main purposes: Click fraud and Bitcoin mining. If running at maximum capacity the ZeroAccess botnet is capable of making a staggering amount of money: in excess of $100,000 a day.”
Sophos has published a report on their research into ZeroAccess, which is available here.