A trojan has been detected which can record Skype calls and send the conversations back to an attacker using an MP3 file.
Symantec researchers have seen the public availability of source code for a trojan that was "essentially acting as a wiretap and compromising confidentiality".
Detected as Trojan.Peskyspy, users could download the trojan through a social engineering tactics such as a successful phishing attack.
Once on a computer, the trojan uses an application that handles audio processes within, and save the call data as an MP3 file.
This keeps the audio file size small, which can speed up the transfer and avoid detection.
The file can then be sent over the internet to a server where the attacker can listen in to the conversation.
"The trojan is targeting Windows API hooks, a technique used to alter the planned behaviour of an application, that Microsoft has intended to be used by audio applications," said a Symantec spokeswoman.
"The trojan compromises the machine and then through the hooking technique is able to eavesdrop on a conversation before it even reaches Skype, or any other audio application."
In a statement, Skype said that harmful viruses and trojans were endemic to the internet, and that it was aware of the trojan in question.
It strongly recommended that users follow security best practice, such as maintaining up-to-date antivirus, using personal firewalls or patching their computers.
