Call it the attack of the zombie refrigerators.

Computer security researchers say they have discovered a large "botnet" which infected internet-connected home appliances and then delivered more than 750,000 malicious emails.

At least one refrigerator was used to create a botnet that sent spam. Credit:AFP

The California security firm Proofpoint, which announced its findings, said this may be the first proven "internet of things" based cyber attack involving "smart" appliances.

Proofpoint said hackers managed to penetrate home-networking routers, connected multimedia centres, televisions and at least one refrigerator to create a botnet — or platform to deliver malicious spam or phishing emails from a device, usually without the owner's knowledge.