1. ActiveX Controls

For years, ActiveX--the technology which dates all the way back to Windows 3.0's OLE (Object Linking and Embedding)?had not one but two majorly pernicious effects on computer users. Folks who use Web sites that run ActiveX applets on their PCs open themselves up to security risks, since an ActiveX control can do pretty much anything it wants on your PC once you'd told it to run. And the fact that ActiveX runs only in Internet Explorer in Windows stunted the growth of alternative browsers and operating systems for years. ActiveX controls still exist, but with some exceptions--mostly related to Microsoft "benefits" like Windows Update and Windows Genuine Advantage--it's easier than ever to ignore them. Thank goodness for that.