windows 7 - what is "cd4f11d23e3716b84c14abcfeaea" and how did it get installed?

Possible Duplicate:
Windows Updates Folders (With Strange Names) in C drive
What are these folders created on my Western Digital 2TB Mirror?

Mystery: Two nights ago, a 20GB file appeared on an almost empty non-OS drive in my computer. I did not install or download it. It has appeared in a drive I only normally use for backups. It will not let me erase it. It has the title cd4f11d23e3716b84c14abcfeaea I can open it but I can't open any of the sub folders. Here is what it looks like when I open it

Can anyone tell me if this is malicious and if so how I can remove it?

Thank you