Between December 23 and January 6, more than 100,000 internet-connected smart “things,” including media players, smart televisions and at least one refrigerator, were part of a network of computers used to send 750,000 spam emails. So says a study just released by enterprise security company Proofpoint. This is the first time anyone in the security industry has proved that devices that are part of the internet of things are being used just as PCs have been for decades—as part of “zombie” networks of computers used to do everything from sending spam to mining bitcoin.

It’s long been known that smart devices are among the most insecure computers on the internet, but it appears that hackers are finally taking advantage of the fact that everything from our toasters to our lightbulbs will soon be internet connected—and ripe for compromising.

“Bot-nets are already a major security concern and the emergence of thingbots may make the situation much worse,” said Proofpoint security manager Dave Knight in a prepared statement.

In the same statement, security analyst Michael Osterman summed it up like this: “Internet-enabled devices represent an enormous threat because they are easy to penetrate, consumers have little incentive to make them more secure, the rapidly growing number of devices can send malicious content almost undetected, few vendors are taking steps to protect against this threat, and the existing security model simply won’t work to solve the problem.”

Naturally, Proofpoint would like to sell its customers a solution to this issue. It’s not clear yet that hacking smart devices has reached the point that consumers need to worry about it, and spam is a largely solved problem in email, but the fact that this kind of hacking is happening shows that the internet of things will have to be secured just like every other computer network—and someone will make a nice bit of money doing so.