When running a botnet, attrition is constant, as security software on PCs finds and eliminates the malicious code that turned the PC into a botnet node. Accordingly, many "botmasters" outsource infections to what's known as pay-per-install (PPI) service providers. Going rates for infecting 1,000 unique PCs with malware range from up to $180 in the United States and Great Britain, from $20 to $160 for other parts of Europe, down to just $7 or $8 in parts of Asia.