Joshua Schichtel of Phoenix, Arizona, was sentenced for renting out more than 72,000 PCs that he had taken over using computer viruses.
Millions of PCs are enrolled in these networks, known as botnets, and many help to send out junk mail messages.
Schichtel's customers installed their own malicious software on the PCs to aid their own cybercrime efforts.
As well as going to prison for 30 months, Schichtel was also sentenced to a three-year supervised release programme that he will serve after leaving jail. The supervision will tightly control his access to computers and the net.
In a brief statement about the case, the US Department of Justice said Schichtel pleaded guilty to one count of selling access to 72,000 machines that formed part of a bigger botnet he controlled.
Schichtel received $1,500 (£939) for handing over control to an unnamed customer.
In 2004, Schichtel was one of four men accused of using botnets to carry out attacks on websites. The charges against them were dropped because the US government failed to file an indictment before a court-imposed deadline.