Virus: locate infected machine

Looks like Conflicker.

See http://esupport.trendmicro.com/solution/en-us/1039145.aspx

Not sure if their advice will apply to your network system or not.

When you say "source of the infection", are you trying to establish which of the computers was infected first before it proliferated through the network (ie. find out what user opened a bad email or inserted a usb flash drive), OR do you mean as dbrunton has assumed (ie. what the actual name of the virus is)?

you can see the path in that infected column looks like C:\windows\system32\
scan that file online.
www.virustotal.com or virscan.org  you will get the name of virus then you can find more information on that virus and also removal instructions.

Downad.AD is the Conficker Worm (as stated by dbrunton), and Mal_DownadJ is the part of it that created the scheduled task so it could execute at a scheduled time and date.

Too slow!  Good you found the culprit but still could do with closing this particular door to stop it arriving via a different route.

Good call with WireShark.  I was actually just in the process of checking out Network Sniffers after reading up again on the details of the number of URLs and Servers that it connects to/with.  I was looking for a Video on the Sophos site by their chief engineer demonstration WireShark at work so I could post back here with the link.  Seems you beat me to it ;-)

Thanks for the help!

If you have the same problem, try this: -
http://www.wireshark.org/download.html

Thank you HKFuey, even though I was too late in suggesting the same utility you actually used yourself to pin down the source.  Just for completeness, if anyone else happens upon this question, the Sophos video that I was originally looking for is here:
http://www.youtube.com/user/SophosLabs#p/u/48/nPKYubm7yeA
Or a better version from the Main Menu > "Adobe Reader Vulnerability Demo" here:
http://www.sophos.com/en-us/security-news-trends/anatomy-of-an-attack.aspx