Aero Snap is a feature of Windows 7 that automatically rearranges your open windows. Although it’s designed to be useful, it can be annoying to have windows move round without your permission. You can, however, easily turn off this feature.
Step 1 Click Start, then click Control Panel.
Step 2 In the Control Panel, click Ease of Access
Step 3 Click Change how your mouse works.
Step 4 Under the Make it easier to manage windows section, tick Prevent windows from being automatically arranged when moved to the edge of the screen.
Step 5 Click OK.