A cybercrime website is offering hundreds of dollars for infecting PCs with malware - and US and UK users are particularly highly prized.

Pay-Per-Install.org stands out as a malware flea market where pushers of Trojan downloaders and tools for evading detection are bargaining with thousands of would-be "affiliates" willing to compromise victims' computers globally and get paid for it.

Top dollar goes to anyone who can compromise computers in the United States. Those who do the dirty work are paid $140 for every 1,000 US. computers they infect, to ready these victims' computers for other types of criminal assaults such as stealing financial data, sending spam or pushing fake antivirus software. The pay-per-install rate is quite high for PCs in the UK, fetching  $110 per 1,000 computers. There's then a bit of a drop: $60 in Italy; $30 in France and just $6 in Asia. Curiously, Russia and several of Russia's neighbors, such as Belarus and Ukraine, are considered off limits.

"They will not pay for installs in Russia or former Soviet Bloc countries," says Kevin Stevens, a researcher at SecureWorks, which recently issued a report delving into the malware bargaining that goes on at Pay-Per-Install.org. The online forum encompasses about 10 distinct entities, such as TrafCash.com and earning4u.com (believed since August to be the new name of InstallsCash), angling for affiliates to do their dirty work to take control of computers they can exploit. "They don't want infection of Russian computers," said Stevens.

Some rogue antivirus software even has an installer component that checks to see if a user has visited sites such as Google.ru or vkontackte.ru, and if so will exit immediately.

Many researchers suspect Russian-speaking kingpins to be the key players at Pay-Per-Install.org, where forum discussions go on in both Russian and English. In addition, the earning4u site, which is among the most notorious, has a Russian IP address.

There's plenty of speculation why big-time malware pushers such as earning4u.com wouldn't want to mess with computers owned by Russians or in countries bordering Russia where many ethnic Russians reside. But the most likely explanation is one put forward by Benjamin Edelman, assistant professor at Harvard Business School in its negotiations, organisations and markets unit.

"Why would Russian law enforcement want to pursue attacks that never hurt Russians?" Edelman said. "By declining to hurt people in their own country, they discourage law enforcement from pursuing them."