"According to security company ESET, the average compromised machine is home to 13 infected files as well as malicious programs from three different malware families. ESET based its findings on scans of more than a half-million PCs using the free online scanner on the company’s Website. In their own way, the results may demonstrate the way attackers are working together to tag-team vulnerable users.
According to ESET, the presence of multiple malware families is the result of the "pay per install" phenomenon, in which cyber-criminals are pushing out malware to computers under their control. " – Content courtesy of Online malware – Compromised Computers Host an Average of 3 Malware Families – eWeek Security Watch