The UK has the highest spyware infection rate of any European country, security vendor Webroot has said in a new report.

The company's quarterly State of Spyware report, based on an international survey of enterprise and consumer PCs, found that spyware infections are again on the rise after a lull last year.

In 2004, many security experts said the spyware problem had reached its peak, and Webroot said it detected a slowdown in infections for the second half of 2005. No longer, however.

"The data we have culled during the past six months unequivocally show that spyware is anything but extinct," said Webroot chief executive C. David Moll, in a statement.

"Spyware is a financially motivated threat and as long as there is a dollar to be had, cyber criminals will do everything possible to steal it."

The UK took over from Ireland at the top of the spyware charts for the second quarter of 2006, with an average of 30.5 pieces of spyware per PC, Webroot said. Ireland followed with 30.3 spies per PC, Lithuania with 29.3 and Latvia with 26.5. The worldwide average was 24.5 spies per PC.

While Webroot and others say the targeting of English-language countries is a big factor upping the infection rate, the US scored lower than the UK with an average of 30 spies per PC.

Ireland, Lithuania and Latvia have scored high on the European list for several quarters because their expanding economies make them better targets, Webroot said.

The problem isn't confined to prosperous Western countries, however - in fact Puerto Rico had the overall highest number of spyware infections detected per PC, with 42.6 per PC on average; Algeria had 38.4 and Bahrain had 35.7.

Consumers account for the highest proportion of infections, at 89 percent overall, but enterprises aren't immune. Based on scans of more than 19,000 enterprise PCs in 71 countries, mostly in the US, Italy, the UK and Belgium, Webroot found that enterprise PCs had 19 spyware infections on average, down slightly from 21.5 the previous quarter.

Australia had the highest average number of spyware programs detected for enterprise PCs, at 37.7. Mexico hit 29.4 and Switzerland hit 21.4.

Among infected enterprise PCs scanned by Webroot, there were 1.3 Trojans present on average, and 40 companies over the last quarter said they'd suffered major security breaches due to spyware infections.

Since about 70 percent of enterprises use anti-spyware software, the relatively steady level of infections show that the software in use might not be effective, Webroot said.

The company pinned the new increase in infections on the introduction of new attack vectors, including social networking sites such as MySpace, and the rise in junk emails loaded with spyware.

Another problem is that the free anti-spyware programs used by most of the public aren't capable of detecting spyware that uses advanced techniques such as rootkits, Webroot said.