Nine out of ten PCs are infected with spyware, new research has found.

After a fall in 2005, spyware infection rates have risen again to their highest level since 2004, thought to be spyware's heyday, according to a recent report by anti-spyware company Webroot Software. 

"Less than a year ago, many so-called internet security experts began claiming that spyware was on the decline and that infection rates would soon drop to the point of extinction," said C David Moll, chief executive at Webroot.

"While the infection rates at that time seemingly supported this theory, the data we have culled during the past six months unequivocally shows that spyware is anything but extinct."

During the second quarter of 2006, Webroot researchers found that 89 per cent of consumer PCs were infected with an average of 30 pieces of spyware, a slight increase from the first quarter of 2006.

New online channels, more sophisticated spyware technology and consumer reliance on free anti-spyware applications are all contributing factors.

Spyware has found fertile ground to propagate among new victims in social networking sites such as MySpace, according to the report.

Meanwhile spammers recognise the extra profitability of adding spyware to their email scams, and criminals are flooding the internet with an increased number of spyware websites to ensnare new victims. 

Webroot has identified 527,136 malicious websites to date. This number marks a substantial increase during the past quarter as the number of identified websites at the close of the first quarter of 2006 was 427,000.