When Win32/Gaobot is run, it copies itself to either the Windows or System directories. In many cases, it adds a value to the registry keys:
This value causes the worm to start when Windows is started. Some variants may also add a Windows Service to attain similar results.
Win32/Gaobot connects to a remote IRC server and joins a specific channel to receive commands. These commands can include actions such as scanning for unpatched machines on the network, downloading and executing remote files, adding and removing local users, retrieving the machine configuration, and updating the worm.
The worm spreads to remote machines by exploiting one or more of eight vulnerabilities. For example, the worm exploits the MS03-026 vulnerability to create a remote shell on the target machine. The worm uses the remote shell to copy and run the worm on a remote machine. The worm uses the eight different vulnerabilities in different ways, but the goal of the worm is consistent: it always attempts to copy and run on the remote machine.
Win32/Gaobot may also spread to machines with weak passwords by enumerating through a hard-coded list of passwords until it gains access. Once access is achieved, the worm copies itself and creates a task on the target machine to run the copy.
Some variants of the worm terminate security products, based on a hard-coded list of process names.
Later variants of the worm include user-mode stealth, which hides the worm's process and file from Task Manager and Windows Explorer.
Later variants of the worm overwrite the Windows host file to block access to different security Web sites.
Take the following steps to help prevent infection on your computer:
Enable a firewall on your computer.
Get the latest computer updates for all your installed software.
Use up-to-date antivirus software.
Limit user privileges on the computer.
Use caution when opening attachments and accepting file transfers.
Use caution when clicking on links to webpages.
Avoid downloading pirated software.
Protect yourself against social engineering attacks.
Use strong passwords.
Enable a firewall on your computer
Use a third-party firewall product or turn on the Microsoft Windows Internet Connection Firewall.
Get the latest computer updates
Updates help protect your computer from viruses, worms, and other threats as they are discovered. It is important to install updates for all the software that is installed in your computer. These are usually available from vendor websites.
You can use the Automatic Updates feature in Windows to automatically download future Microsoft security updates while your computer is on and connected to the Internet.
Use up-to-date antivirus software
Limit user privileges on the computer
Starting with Windows Vista and Windows 7, Microsoft introduced User Account Control (UAC), which, when enabled, allowed users to run with least user privileges. This scenario limits the possibility of attacks by malware and other threats that require administrative privileges to run.
You can configure UAC in your computer to meet your preferences:
Use caution when opening attachments and accepting file transfers
Exercise caution with email and attachments received from unknown sources, or received unexpectedly from known sources. Use extreme caution when accepting file transfers from known or unknown sources.
Use caution when clicking on links to webpages
Exercise caution with links to webpages that you receive from unknown sources, especially if the links are to a webpage that you are not familiar with, unsure of the destination of, or suspicious of. Malicious software may be installed in your computer simply by visiting a webpage with harmful content.
Avoid downloading pirated software
Threats may also be bundled with software and files that are available for download on various torrent sites. Downloading "cracked" or "pirated" software from these sites carries not only the risk of being infected with malware, but is also illegal. For more information, see 'The risks of obtaining and using pirated software
Protect yourself from social engineering attacks
While attackers may attempt to exploit vulnerabilities in hardware or software to compromise a computer, they also attempt to exploit vulnerabilities in human behavior to do the same. When an attacker attempts to take advantage of human behavior to persuade the affected user to perform an action of the attacker's choice, it is known as 'social engineering'. Essentially, social engineering is an attack against the human interface of the targeted computer. For more information, see 'What is social engineering?
Use strong passwords
Attackers may try to gain access to your Windows account by guessing your password. It is therefore important that you use a strong password – one that cannot be easily guessed by an attacker. A strong password is one that has at least eight characters, and combines letters, numbers, and symbols. For more information, see http://www.microsoft.com/protect/yourself/password/create.mspx