You can waste time creating a new MBR then trying to clean ALL the infected files from not just the rootkit but it’s buddies as well. Save your clients time and money and their security. Backup/format/reload.
An antivirus of its own
Just like Sinowal, TDL-4 is a bootkit, which means that it infects the MBR in order to launch itself, thus ensuring that malicious code will run prior to operating system start. This is a classic method used by downloaders which ensures a longer malware lifecycle and makes it less visible to most security programs.
TDL nimbly hides both itself and the malicious programs that it downloads from antivirus products. To prevent other malicious programs not associated with TDL from attracting the attention of users of the infected machine, TDL-4 can now delete them. Not all of them, of course, just the most common.
TDSS module code which searches the system registry for other malicious programs
TDSS contains code to remove approximately 20 malicious programs, including Gbot, ZeuS, Clishmic, Optima, etc. TDSS scans the registry, searches for specific file names, blacklists the addresses of the command and control centers of other botnets and prevents victim machines from contacting them.
This ‘antivirus’ actually helps TDSS; on the one hand, it fights cybercrime competition, while on the other hand it protects TDSS and associated malware against undesirable interactions that could be caused by other malware on the infected machine.
Which malicious programs does TDL-4 itself download? Since the beginning of this year, the botnet has installed nearly 30 additional malicious programs, including fake antivirus programs, adware, and the Pushdo spambot.
Notably, TDL-4 doesn’t delete itself following installation of other malware, and can at any time use the r.dll module to delete malware it has downloaded.
Botnet access to the Kad network
One of the most outstanding new features of TDL-4 is the kad.dll module, which allows the TDSS botnet to access the Kad network. So what do the cybercriminals want with a publicly accessible file exchange network?
We have known about botnets controlled via P2P for some time now, although until now, these were closed protocol connections created by the cybercriminals themselves. In contrast, TDSS uses a public P2P network in order to transmit commands to all infected computers in the botnet. The initial steps of how TDSS makes use of Kad are given below:
The cybercriminals make a file called ktzerules accessible on the Kad network. The file is encrypted and contains a list of commands for TDSS.
Computers infected with TDSS receive the command to download and install the kad.dll module.
Once installed, kad.dll downloads the file nodes.dat, which contains the publicly accessible list of IP addresses of Kad network servers and clients.
The kad.dll module then sends a request to the Kad network to search for the ktzerules file.
Once the ktzerules files has been downloaded and encrypted, kad.dll runs the commands which ktzerules contains.
Encrypted kad.dill updates found on the Kad network
Below is a list of commands from an encrypted ktzerules file.
SearchCfg – search Kad for a new ktzerules file
LoadExe – download and run the executable file
ConfigWrite – write to cfg.ini
Search – search Kad for a file
Publish – publish a file on Kad
Knock – upload a new nodes.dat file to the C&C which contains a list of Kad server and clients IP addresses, including those infected with TDSS.