It will be helpful to understand if you could please give the exact details of the following :-
1} Which McAfee software are you using ? McAfee Home version ? The SaaS Version ? Virus Scan Enterprise ?
2} What is the exact name of the infection you got in the alert ?
3} When you saw the detected alert, did McAfee quarantine or removed it ?
Moved to Malware Discussion > Corporate User Assistance for better attention.
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Was this Blaster or MSBlaster? Either way, if your system is totally up to date with all updates critical and optional it shouldn't be a problem as Microsoft's monthly Malicious Software Removal Tool scan should have removed it.
Knowing what operating system this is would help. Try disabling System Restore temporarily. Go to Start/Run and type in temp and click Enter or OK
Go to Edit and click Select All
Click Shift/Delete and OK any prompts. Most will delete, some may not that's OK.
Do the same again this time entering %temp%.
See if it still exists after getting totally up to date and doing the above.
By the way if the system is up to date, you can check if the MRT ran the last time by looking for KB890930 in your installed updates, it would have run around 11 January.
If it's not there you can install & run it separately here: http://www.microsoft.com/downloads/en/details.aspx?FamilyId=AD724AE0-E72D-4F54-9 AB3-75B8EB148356&displaylang=en
If this is a 64-bit system use this one: http://www.microsoft.com/downloads/en/details.aspx?FamilyId=585D2BDE-367F-495E-9 4E7-6349F4EFFC74&displaylang=en