how do i handle a virus found

Stop and think.
It is possible it is what is called a false positive.
Do not run the file at this point.

Do you know where you got the file from?
Is the file important to you? If so can you get a fresh copy?

Get a second opinion.
Up load the file to:
http://www.virustotal.com/en/indexx.html
and / or
http://virusscan.jotti.org/

They will run tests on the file by various antivirus products and tell you if other vendors are seeing a problem and help you decide what to do.

Now to answer question you did Not ask first,
ClamWin CAN NOT CLEAN a virus out of a file!!!

It has 3 settings, the Default is Report, which you have seen, the others are Quarantine, and Delete.
It can be set to Quarantine or Delete automatically, but since you appear to be dealing with only one file on your flash drive, G:\Msinfo.msi , you should just delete it yourself, manually [hit the delete key when the file is selected]

That is the best way to do it.

[Now to the question you Did ask, if you Really need to know how to make ClamWin Quarantine or Delete Automatically go to Tools->Preferences->General->Infected Files and choose Remove or Move to Quarantine Folder and click ok ]

Again, since ClamWin cannot clean the file itself it is best to just leave it in its default settings for future use, and just delete the file yourself.

Tim