XP: Folders Don't Open On Double-click, Search Window Opens Instead

I had some spyware/viruses/malware recently, and they've now all been cleaned up with internet security software, but I still have a lingering problem: when I double-click on a folder, instead of the folder opening, a new window opens and it's a search window, with the destination folder (ie the one I just clicked on) as a value in the parameter "look in:". The only way I can just open a folder is to right-click, and select open.

When I right-click on a folder, the menu reads: "Search (bolded) / Open / Explore" etc. which doesn't seem right.

I tried to fix it by changing some options in Tools -> Folder Options -> File Types. There are two kinds of folder, "File Folder" and "Folder". In the advanced options for "File Folder", the only action it lists is "find"... I'm not sure if this is where the problem is or if this is normal? I tried to add a new action, but it wanted me to select an application to perform the action and I have no idea... In the advanced options for "Folder", it looks to be normal, it lists the actions "explore" and "open" (bolded).

The only folder that seems unaffected by this problem is the "Documents" folder on the desktop, and any shortcuts that point to folders.