Well, now there's a computer Trojan horse called Trojan.Peskyspy that has the ability to do just that, record conversations via Skype VoIP (Voice over IP).
It's not the first time that Trojans have been written to target Skype users but it's definitely the first time that a Skype Trojan has the ability to record Skype calls. Security experts have identified that Skype does not have any new vulnerability issues, but rather the Trojan.Peskyspy infection is able to listen to data traveling between the Skype processes and the audio device used for transmitting voice or sound.
Swiss programmer Ruben Unteregger developed Trojan.Peskyspy and released the source code on his website megapanzer(dot)com. According to Unteregger's interview with gulli.com, he created Trojan.Peskyspy for Swiss and probably German law enforcement agencies.