The Pew report (PDF file), written by associate director Susannah Fox, highlights the increased awareness of privacy and other threats presented by adware and spyware programs.
Overall, the projects survey found that nine out of 10 of Internet users have made at least one change in their online behavior to avoid unwanted software programs.
These behavior changes include not opening e-mail attachments unless they are sure these documents are safe or not visiting specific Web sites that they fear might deposit unwanted programs on their computers.
One quarter of the respondents have stopped using file-sharing programs because of the way unwanted adware programs are bundled into the peer-to-peer applications.
About 20 percent of the respondents said they switched Web browsers to avoid software intrusions.
"After hearing descriptions of spyware and adware, 43 percent of Internet users, or about 59 million American adults, say they have had one of these programs on their home computer," Fox said, noting that the numbers are probably a "conservative estimate" because the survey may have been the first time that respondents had heard definitions of the programs.
"In addition, there are significant gaps between peoples perceptions and the reality of what is on their computers, and there is a very strong likelihood that a big portion of those who have had computer problems have been victimized by spyware or more aggressive computer viruses without their knowing the cause of their problems," Fox added.
In the report, Fox draws a clear distinction between spyware and adware, defining spyware as software that is placed secretly on a computer in order to track a users behavior and report back to a central source.
"Spywares reputation is like that of a Peeping Tom or, at worst, a thief. It is almost universally derided and despised. It seems that no user wants to have spyware on her computer and few companies want to be associated with it," she said.
On the other hand, Fox described adware as software that comes bundled as a package with programs that consumers download. In some cases, Internet users check off on a "user agreement" before the download begins, "though our survey shows that in many cases people are not paying much attention to those agreements," she said.
During the survey, Fox discovered that most Internet users think symptoms of spyware are serious problems rather than minor annoyances. "Millions of Internet users have firsthand experience with computer problems related to software intrusions, and while many express confidence and knowledge of the issues, most think more should be done to guard against spyware and to notify people about adware."