By hijacking a working spam network, US researchers have uncovered some of the economics of being a junk mailer.

For their month-long study the seven-strong team of computer scientists infiltrated the Storm network that uses hijacked home computers as relays for junk mail.

At its height Storm was believed to have more than one million machines under its control.

"The best way to measure spam is to be a spammer," wrote the researchers in a paper describing their work.

They created several so-called "proxy bots" that acted as conduits of information between the command and control system for Storm and the hijacked home PCs that actually send out junk mail.

The team used these machines to control a total of 75,869 hijacked machines and routed their own fake spam campaigns through them.