BleepingComputer.com: I'm infected with Win32/Spy.Ursnif.A virus

I'm running XP and have been receiving the following error message from eset NOD32 for four days now:

Object:
C:\WINDOWS\system32\winlogon.exe
Threat:
Win32/Spy.Ursnif.A Virus
Comment:
Event occurred during at attempt to run the file by the application:
C:\Program Files\Google\Update\GoogleUpdate.exe.

When I try to clean or delete, I am informed that this object cannot be cleaned. I tried running malwarebytes without effect. I read someone recommending ComboFix, but it is stressed that that not be used without guidance. I'm getting the feeling this is not good news for me and my passwords, so here is my plea for help. Thanks in advance.

Hello geomoo, and to BleepingComputer!

Not to stress you any further, but I am obliged to post the following first

Please note: ComboFix is an extremely powerful tool which should only be used when instructed to do so by someone who has been properly trained. ComboFix is intended by its creator to be "used under the guidance and supervision of an expert." It is NOT for private use. Please read Combofix's Disclaimer. Using this tool incorrectly could lead to disastrous problems with your operating system such as preventing it from ever starting again.


Before we start fixing anything you should print out these instructions or copy them to a NotePad file so they will be accessible. Some steps will require you to disconnect from the Internet or use Safe Mode and you will not have access to this page.

ATF-CLEANER
------------------
Please download ATF Cleaner by Atribune. (This program is for XP and Windows 2000 only)

Double-click ATF-Cleaner.exe to run the program.
Under Main "Select Files to Delete" choose: Select All.
Click the Empty Selected button.

If you use Firefox browser

Click Firefox at the top and choose: Select All
Click the Empty Selected button.
NOTE: If you would like to keep your saved passwords, please click No at the prompt.

If you use Opera browser

Click Opera at the top and choose: Select All
Click the Empty Selected button.
NOTE: If you would like to keep your saved passwords, please click No at the prompt.

Click Exit on the Main menu to close the program.
For Technical Support, double-click the e-mail address located at the bottom of each menu.


DR. WEB CUREIT
----------------------
Please download Dr.Web CureIt and save it to your desktop. DO NOT perform a scan yet.
alternate download link
Note: The file will be randomly named (i.e. 5mkuvc4z.exe).

Reboot your computer in "Safe Mode" using the F8 method. To do this, restart your computer and after hearing your computer beep once during startup (but before the Windows icon appears) press the F8 key repeatedly. A menu will appear with several options. Use the arrow keys to navigate and select the option to run Windows in Safe Mode.

Scan with Dr.Web CureIt as follows:

• Double-click on the randomly named file to open the program and click Start. (There is no need to update if you just downloaded the most current version
  
• Read the Virus check by DrWeb scanner prompt and click Ok where asked to Start scan now? Allow the setup.exe to load if asked by any of your security programs.
  
• The Express scan will automatically begin.
  (This is a short scan of files currently running in memory, boot sectors, and targeted folders).
  
• If prompted to dowload the Full version Free Trial, ignore and click the X to close the window.
  
• If an infected object is found, you will be prompted to move anything that cannot be cured. Click Yes to All. (This will move any detected files to the C:\Documents and Settings\userprofile\DoctorWeb\Quarantine folder if they can't be cured)
  
• After the Express Scan is finished, put a check next to Complete scan to scan all local disks and removable media.
  
• In the top menu, click Settings > Change settings, and uncheck "Heuristic analysis" under the "Scanning" tab, then click Apply, Ok.
  
• Back at the main window, click the green arrow "Start Scanning" button on the right under the Dr.Web logo.
  
• Please be patient as this scan could take a long time to complete.
  
• When the scan has finished, a message will be displayed at the bottom indicating if any viruses were found.
  
• Click Select All, then choose Cure > Move incurable.
  
• In the top menu, click file and choose save report list.
  
• Save the DrWeb.csv report to your desktop.
  
• Exit Dr.Web Cureit when done.
  
• Important! Reboot your computer because it could be possible that files in use will be moved/deleted during reboot.
  
• After reboot, post the contents of the log from Dr.Web in your next reply. (You can use Notepad to open the DrWeb.cvs report)