Is this a security risk?

I found a worm (W32 Rontokbro@mm) that was detected by Norton and was quarantined. I opened the email that contained the infection but did not run the attachment. It was detected in the temporary internet files folder in Windows 7. My question is whether this is a security risk and should I reformat the computer.

 

SusieQueue, welcome to Majorgeeks.

Work your way through the Read And Run Me.
Follow the directions.
If you have issues, make a note of the same- and continue on to the next step of instructions.
Once you have the requested logs, please attach the same, in a new thread started in MalwareRemoval.
Mention any Issues, you may have faced running the scanners /obtaining logs.

Cheers..