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Sounds to me like you have a virus that uses the RPC service to shut you down. If you don't have a firewall this is quite likely.

When W32.Blaster.Worm is executed, it does the following:


Checks to see whether a computer is already infected and whether the worm is running. If so, the worm will not infect the computer a second time.


Adds the value:

"windows auto update"="msblast.exe"

to the registry key:

HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\Run

so that the worm runs when you start Windows.


Generates an IP address and attempts to infect the computer that has that address. The IP address is generated according to the following algorithms:

For 40% of the time, the generated IP address is of the form A.B.C.0, where A and B are equal to the first two parts of the infected computer's IP address.

C is also calculated by the third part of the infected system's IP address; however, for 40% of the time the worm checks whether C is greater than 20. If so, a random value less than 20 is subtracted from C. Once the IP address is calculated, the worm will attempt to find and exploit a computer with the IP address A.B.C.0.

The worm will then increment the 0 part of the IP address by 1, attempting to find and exploit other computers based on the new IP address, until it reaches 254.


With a probability of 60%, the generated IP address is completely random.


Sends data on TCP port 135 that may exploit the DCOM RPC vulnerability. The worm sends one of two types of data: either to exploit Windows XP or Windows 2000.

For 80% of the time, Windows XP data will be sent; and for 20% of the time, the Windows 2000 data will be sent.

NOTES:
The local subnet will become saturated with port 135 requests.
While W32.Blaster.Worm cannot spread to the Windows NT or Windows Server 2003, unpatched computers running these operating systems may crash as a result of the worm's attempts to exploit them. However, if the worm is manually placed and executed on a computer running these operating systems, it can run and spread.
Due to the random nature of how the worm constructs the exploit data, this may cause the RPC service to crash if it receives incorrect data. This may manifest as svchost.exe, generating errors as a result of the incorrect data.
If the RPC service crashes, the default procedure under Windows XP and Windows Server 2003 is to restart the computer. To disable this feature, see step one of the Removal Instructions below.


Uses Cmd.exe to create a hidden remote shell process that will listen on TCP port 4444, allowing an attacker to issue remote commands on an infected system.


Listens on UDP port 69. When the worm receives a request from a computer to which it was able to connect using the DCOM RPC exploit, it will send msblast.exe to that computer and tell it to execute the worm.


If the current date is the 16th through the end of the month for the months of January to August, or if the current month is September through December, the worm will attempt to perform a DoS on Windows Update. However, the attempt to perform the DoS will succeed only if one the following conditions is true:
The worm runs on a Windows XP computer that was either infected or restarted during the payload period.
The worm runs on a Windows 2000 computer that was infected during the payload period and has not been restarted since it was infected.
The worm runs on a Windows 2000 computer that has been restarted since it was infected, during the payload period, and the currently logged in user is Administrator.


The DoS traffic has the following characteristics:
Is a SYN flood on port 80 of windowsupdate.com.
Tries to send 50 HTTP packets every second.
Each packet is 40 bytes in length.
If the worm cannot find a DNS entry for windowsupdate.com, it uses a destination address of 255.255.255.255.

Some fixed characteristics of the TCP and IP headers are:
IP identification = 256
Time to Live = 128
Source IP address = a.b.x.y, where a.b are from the host ip and x.y are random. In some cases, a.b are random.
Destination IP address = dns resolution of "windowsupdate.com"
TCP Source port is between 1000 and 1999
TCP Destination port = 80
TCP Sequence number always has the two low bytes set to 0; the 2 high bytes are random.
TCP Window size = 16384


The worm contains the following text, which is never displayed:

I just want to say LOVE YOU SAN!!
billy gates why do you make this possible ? Stop making money and fix your software!!

Download the FixBlast.exe file from:

http://securityresponse.symantec.com/av ... xBlast.exe



Save the file to a convenient location, such as your downloads folder or the Windows Desktop (or removable media that is known to be uninfected, if possible).
To check the authenticity of the digital signature, refer to the section, "Digital signature."
Close all the running programs before running the tool.
If you are running Windows XP, then disable System Restore. Refer to the section, "System Restore option in Windows Me/XP," for additional details.


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CAUTION: If you are running Windows XP, we strongly recommend that you do not skip this step. The removal procedure may be unsuccessful if Windows XP System Restore is not disabled, because Windows prevents outside programs from modifying System Restore.
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Double-click the FixBlast.exe file to start the removal tool.
Click Start to begin the process, and then allow the tool to run.


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Note: If, when running the tool, you see a message that the tool was not able to remove one or more files, run the tool in Safe mode. Shut down the computer, turn off the power, and wait 30 seconds. Restart the computer in Safe mode and then run the tool again. All the Windows 32-bit operating systems, except Windows NT, can be restarted in Safe mode. For instructions, read the document "How to start the computer in Safe Mode."
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Restart the computer.
Run the removal tool again to ensure that the system is clean.
If you are running Windows XP, then re-enable System Restore.
Run LiveUpdate to make sure that you are using the most current virus definitions.