Crooks are using Skype to spread malware that enslaves victims' computers and makes them mine bitcoins, according to Kaspersky Lab.
The scam sees victims sent messages such as "this my favourite picture of you" via Skype, tricking them into downloading a virus dropper from a server in India.
Once infected, the PC is sent various pieces of malware, one of which is designed to turn it into a bitcoin mining slave, harvesting coins for the crooks.
Bitcoins - which have soared in value over the last few weeks - are created by using computing power to solve cryptographic "proof-of-work" problems, with the miner rewarded with coins.
In a blog post, Kaspersky's Dmitry Bestuzhev says that the Trojan is getting more than 2000 clicks an hour, with most potential victims coming from Italy then Russia, Poland, Costa Rica, Spain, Germany and Ukraine.
With most anti-virus programs failing to pick up the malware, Bestuzhev advises people to check on their CPU because "if you see your machine is working hard, using all available CPU resources, you may be infected".