By default, the fill handle and drag-and-drop editing is turned on in Excel so that you can drag the mouse to move and copy cells by doing the following:
Move a cell or range of cells by positioning the mouse pointer on a cell or cell range border so that it changes to a move pointer , and then dragging the cell to another location.
Copy a cell or range of cells by holding down CTRL while you position the mouse pointer on a cell or cell range border so that it changes to a copy pointer , and then dragging the cell or range of cells to another location.
Drag the fill handle to copy data or to fill adjacent cells with a series of data.
You can turn this option on or off as needed by doing the following:
Click File > Options.
In Excel 2007 only: Click the Microsoft Office Button , and then click Excel Options.
In the Advanced category, under Editing options, select or clear the Enable fill handle and cell drag-and-drop check box.
Note: To help prevent replacing existing data when you drag the fill handle, make sure that the Alert before overwriting cells check box is selected. If you do not want Excel to display a message about overwriting non-blank cells, you can clear this check box.