Skype and Microsoft OneCare seem to have a problem to solve. You probably don't have a trojan in your computer.
Trojan:Win32/Vundo.gen!D is Quarantined OneCare says after scanning the PC.
To find out more I created a support log and found this information.
Windows Live OneCare found potentially harmful or unwanted software on your computer.
Threat Name: Trojan:Win32/Vundo.gen!D
File Name: pid:1200
Threat Severity: Severe
Threat Category: Trojan
Threat found by On Demand Scan: (ANTIVIRUS_ONDEMAND)
Threat Status: Quarantined
Still it did not say anything about what and where this was. I then figured out that Skype was closed each time after a scan and obviously OneCare think Skype does something it should not do. Let's see if it is Microsoft or Skype that fixes this as there are no Trojan really there and there is no unwanted software that should be stopped from running.
Update: Problem is now solved by Microsoft.