Panda said it arrived at the figure after analysing data gathered from an online scanning utility. Chief technology officer Patrick Hinojosa said similar studies had found that around 90 percent of computers are infested with spyware.
"Spyware is installed by many different methods and the infection is not usually visible to the user. These factors increase the infection rate for this type of malware," said Hinojosa.
Panda's findings do not surprise James Turner, security analyst at Frost & Sullivan, who said one of the difficulties when calculating spyware infestation was defining what was spyware and what was not.
"One of the things that fall into this category are cookies. You can say cookies from one particular site are spyware while cookies from another -- such as Hotmail for instance -- are not. There have been cases where an anti spyware company has been taken to court by another company claiming its software is legitimate," said Turner.
Additionally, Turner said, until anti-spyware utilities are easier to use, the majority of Internet users will not be able to adequately protect themselves.
"It is hard for people to draw a line in the sand and say these cookies are ok and those are not ok. At that point it gets quite technical because the tools have not made it simple enough yet. It is still a new and emerging area," said Turner.