In a novel twist on cold calling, an Internet-connected fridge has been discovered as part of a botnet sending over 750,000 spam e-mails.

Do you keep your spam in the pantry? In an undesirable consequence of the move to "Internet of things" and so-called smart appliances, a refrigerator has been left out in the cold after being caught contributing to a botnet attack which generated over 750,000 spam e-mails.

The Internet of things supposedly brings convenience, allowing devices to call for service in the event of malfunction, or tweet energy usage updates to you, or advise that your milk is about to go off and you need to buy more.

Yet, with this rise of convenience comes the reality that devices are being placed online which typically have little to no malware protection. As has been seen in recent times, many home users do not even know to change the default passwords on their Internet-connected cameras. So too this lack of prudence now has extended to a kitchen near you.

Security firm Proofpoint discovere a botnet attack which ran over 23rd December 2014 and 6th January 2015 which incorporated over 100,000 devices. These devices included multimedia centres, routers, televisions and at least one refrigerator - all Internet-connected devices that proved to be explotable. Over 25% were not conventional computers or mobile devices.

The botnet sent out over 750,000 e-mails during this period, with careful coordination such that each device sent out no more than 10 e-mails.

Proofpoint noted the bulk of devices were not subjected to any sophisticated attack but simply were left open on public networks with default passwords.

Advocates of the Internet of things predict over 200 million devices will be Internet-connected by 2020 meaning that without prudence this problem will only increase.