What source port do the packets have? 60661 is a ephemeral port, so it's gonna be pretty tough to determine, by destination port number alone, what service they are attempting to reach (not that a source port would magically clear things up either). Could you post a few sample lines from your firewall log, tcpdump output, etc?
With the info we have so far, this could be anything - even something as harmless as transmissions to a
Limewire servent that the previous user of your IP had running. There also
isn't any breakout targetting that port at the time of this post, FWIW.