Wheelmouse takes control

Windows 98 system. IntelliMouse 1.A. When I accidentally click the wheel in the middle of the mouse, a black triangle appears on the screen and I’m placed in a perpetual selection mode in whatever program I initiated this in, typically Excel. I try Esc, does nothing. I can get to other programs by clicking on their icon at the bottom of my screen. The only way out of the original program’s dilemma is Ctrl\Alt\Del and shutting down the “offending” application. Any easier way to this?