Online consumers think ad-serving software is a widespread problem but generally don't understand how it works and why their computers get infected, although many admit to downloading free programs without reading end-user license agreements, according to a Ponemon Institute study, MediaPost reports. Some 84 percent of respondents said their computers have been infected with spyware in the last year, according to the Unisys-sponsored survey of 1,944 consumers who are online at least an hour each day.

Among those infected users, 42 percent had "no idea" how the unwanted programs got in their computer, although 38 percent attributed it to downloading free software; 8 percent said a spyware program downloaded automatically when they visited a site.

Some 61 percent of respondents didn't remember consenting to downloading adware, and almost all (97 percent) didn't recall giving permission for spyware. Ninety percent of respondents said they had downloaded free programs, mostly music file-shares and games. And 87 percent said they don't read license agreements.