Paint.NET is a legitimate program, and one which is frequently recommended in these forums. I downloaded a copy from download.com, and while I don't have Prevx my own scanners found nothing after the download or during installation. Turning to Prevx, I searched their database and found one match, but it clearly identified as "Safe, this is a software installation utility." Thus, I consider it a likely false positive and notify Prevx technical support. They can look into it and either confirm the alert or release an update to resolve the false alarm.
As to the problem of editing your pictures, Paint.Net likely reassociated the file types with itself so that they open automatically with the new image editor. Since the installation didn't complete it can't open the files. If you opt not to complete the Paint.Net installation you'll need to right-click one of the files, select Open With, and choose the program of your choice from the list, being sure to check 'Always use this program to open files of this type' before clicking OK. You'll have to do that with each file type. (JPG, GIF, BMP, etc.)
Finally, what program displayed the final alert message to remove your hard drive? Prevx may have displayed that as a precaution or it could have been your computer identifying your hard drive as failing. (See the S.M.A.R.T technology.) It's important to know which one it is in case there is a problem.
John
It was suggested that I may get more responces if I moved this question to this Forum
Paint.NET 3.08 Critical Alert
by radcad92 - 6/21/07 10:49 PM
The June 19, 2007 CNET Download Dispatch had a new review for:
Digital Photography
Paint.NET 3.08
License: Free
File size: 1.36MB
Minimum requirements: Windows XP/2003 Server/Vista, Microsoft .NET Framework 2.0
Category: Image Editing
Editor's review of Paint.NET 5 STARS
User reviews of Paint.NET 4.5 STARS
On this recommendation I downloaded the program and immediatly recieved a critical alert from Prevx 2.0 advising:
PAINTDOTNET.MSI
This Excel file has a file size of 4,657,152 bytes, it is most frequently called PAINTDOTNET.MSI and is most frequently located in the %temp%\pdnsetup\ folder.
This file is considered unsafe. It was first seen on Saturday, Jun 2 2007. It has been seen frequently by 60 users in this section of the community. The file has only been seen in the UNITED STATES.
PAINTDOTNET.MSI has been seen to perform the following behaviors:
- This Process Creates Other Processes
- This Process is linked to a Software Installation
- This Process Deletes Other Processes
PAINTDOTNET.MSI has been the subject of the following behaviors:
- Process creation
- Process deletion
- The process is executed as part of a software installation
Needless to say I blocked the install. Could you please tell me if this is a false alarm. This program sounds like it could replace about 3 or more of my image editors. Thank You
Since I posted this I have been unable to edit any of my photos or access any of my image editors. I did a virus & spysweep. When I rebooted I recieved a WARNING: Immediatly back up all data bases & remove hard drive. So I bailed, shut down & am using a different PC.

Chowhound
Comic Vine
GameFAQs
GameSpot
Giant Bomb
TechRepublic