How to remove Conficker virus

Conficker has five known variants and can utilise the various versions to help itself spread fast and via different vectors. Looking at the research done by the Conficker Work Group, you find that the major antivirus vendors have published a variety of repair tools that may clean the virus better than anti-virus alone. Furthermore, you start reading the fine print in the Microsoft Knowledge Base article on Conficker and you see that there is a Group Policy Object (GPO) that can be used to help stop the propagation of the worm.

Now what? First up: get the GPO in place as soon as possible and make sure you enforce it to all Organisational Units. This is not the right time to block inheritance of a policy! Next, you need to test how best to clean an infected machine. Typically, running a couple of tools (one being a full scan of the anti-virus) to find and clean the infection, then rebooting, then running the anti-virus again (full scan), along with having the GPO in place, will help clean and stop the spreading. Start with systems that are showing the account lockout traffic in your logs to focus efforts on known infected machines.

Day five: Oh man. This is the worst day ever!

You see that the number of infected machines is much smaller, but the account lockouts are more frequent. Be patient! Keep scanning and cleaning. It will get better, but it takes persistence.

Day eight: Things are looking better

Finally, things start to calm down and you only see a few computers infected every day. It starts to sink in that this may never fully go away, so you start looking ahead and how to keep the monitoring process ongoing.

Day ten: Keep scanning!

You implement procedures for your operational staff to scan the logs and look for infected machines every couple of hours. Staff should be dispatched to clean machines as soon as they are discovered.

Today: Hold your breath!

But not for too long! See instead if you can focus on doing some forensics and post-mortem analysis to see what you can do better next time. Some things to consider:

• How was the incident handled? Was it clear that an incident manager was designated to be in charge?
• Do you have an incident handling policy? Was it followed? Did it work?
• How was communication to: staff involved in the incident, other IT groups, management, and end users?
• How easy was it to contain computers with the virus? Is your network architecture able to shut down parts of the network easily to isolate virus-infected segments?

Wrapping up

Of course, an ounce of prevention is worth a pound of cure. Here are some thoughts about how to prevent this from running rampant in your organization.

First and foremost, make sure you are patched. It only takes one computer in to get infected before Conficker will let loose everywhere using its other infection vectors. Secondly, try to have a spyware tool in use with your anti-virus tools. The results can be mixed (or non-existent) if you don’t have both in play.

And as with anything, have your incident response procedures up to date and vetted. If you don’t have these processes in place, then you may get too many incident managers running the show and soon become counter-productive. Communication can get muddled, and worse, you may not have enough communication.

Westphal is a 16 year information technology professional with specific experience in the area of information security. She is currently employed as the CISO of the Arizona Department of Economic Security. Skilled in troubleshooting and process analysis, specific expertise in security areas includes forensics, operating system and network security, intrusion detection, incident handling, vulnerability analysis and policy development. Wetphal has been a CISSP since 2001 and a CISA since 2008. You can reach her at kmwestphal@cox.net.