Don't most computers today have a built in Mic? Maybe not for desktops but I think most laptops and notebooks have mics built in. At least both my Asus laptops do and the newest being a 2k13.
My oldest laptop is my testing dummy, through an old exploit on XP and Win7 media player I was able to exploit the Win7 Asus, gaining access to turn the Mic on and specifying how many seconds I wanted to record. Gaining file access, deleting and creating directories and turning on the camera and recording live.