Win32/Msblast threat description - Microsoft Security Intelligence

Threat behavior

When Win32/MSblast variants run, they create a registry entry under the key HKEY_LOCAL_MACHINE\Software\Microsoft\Windows\CurrentVersion\Run, so that the worm automatically starts when the system reboots.

The worm then attempts to spread to other systems on the Internet by selecting an IP address, either at random or based on the IP of the infected system, and incrementing that address. The worm attempts to connect to TCP port 135 on the target system and send exploit communication sequence. If the connection is established and the target computer is an unpatched Windows 2000 or Windows XP system, the worm spreads through TCP port 4444 and UDP port 69. The worm skips any IP address that has a part equal to 255.

The worm may perform other actions, including:

DoS attacks against Web sites, including windowsupdate.com, kimble.org, or tuiasi.ro, if the day of the month is greater than 15 or the month of the year is greater than 8.
Changing the Internet Explorer home page.
Opening a backdoor program, listening at a random TCP port, that allows attackers to gain access to the infected system, and reports the port number and infected system IP address to a remote server.

Prevention

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 Web pages.
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 Web sites.

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

Most antivirus software can detect and prevent infection by known malicious software. To help protect you from infection, you should always run antivirus software, such as Microsoft Security Essentials, that is updated with the latest signature files. For more information, see http://www.microsoft.com/security/antivirus/av.aspx.

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 e-mail 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 Web pages

Exercise caution with links to Web pages that you receive from unknown sources, especially if the links are to a Web page 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 Web page 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 8 characters, and combines letters, numbers, and symbols. For more information, see http://www.microsoft.com/protect/yourself/password/create.mspx.

Win32/Msblast

Summary

What to do now

Recovering from recurring infections on a network

Removing the threat

Technical information