Protecting Your Game From Itself

Under certain circumstances, the game can clobber its own data files, for example killing or vampirizing Mrs. Crumplebottom. Certain modding tools can be misused to produce the same effect, such as modifying resources in situ rather than cloning them. Apparently, BodyShop itself can be used to delete the ugly Maxis clothes, destroying the data files containing them in the process.
To prevent this:

1. Navigate to Program Files/EA Games/. That's Program Files, not My Documents.
2. Start a Search based on this folder by any method you prefer. I like Ctrl-F.
3. Click "All Files and Folders."
4. Type *.package in the Filename box.
5. Make sure that the box to include subfolders is checked (under Advanced Options).
6. Click the "Search" button.
7. Wait a while.
8. When the search is done, select all the files in one big batch. I use Ctrl-A.
9. Right click on one file and pick "Properties" from the context menu.
10. In the Properties dialog, click the box next to "Read Only" until a check mark appears.
11. Click "Ok."
12. Wait a while.

Your files are now safe from the game, yourself, and BodyShop!
Zirconia Wolf also suggests doing this procedure on your Downloads folder. That's My Documents/EA Games/The Sims 2/Downloads, not any other file or folder associated with the game, and definitely not the Neighborhoods folder, or your game won't be able to Save!
When to reverse this: Remember to unprotect the files before applying a Maxis patch or uninstalling the game.