When you hold down the Ctrl key and left-click to select multiple files it's easy to accidently move the mouse and copy all the selected files to the same folder. You can avoid this by setting Windows to select a file when the cursor hovers over it. You can still use the Ctrl button to select multiple files but now without any risk of copying.

Click on the Tools menu, Folder Options and select the General tab. Click the option Single-click to open an item and the option below it 'Underline icon titles only when I point at them'. Click OK. To select several files hold down the Ctrl button, move the cursor over the files and wait until they are selected. If you select a file by accident, hover the cursor over it again to deselect it.