My boyfriend received one of these kinds of calls a few weeks ago and I just couldn't help but giggle in the background. He's like, a master linux sys admin and he decided to play with them a little bit as well.
The phone conversation (not verbatim):
Scammer: "We have been informed that you have malware on your computer and you need our software!"
Boyfriend: "O rly? How do you know this?"
Sc: "We are monitoring your computer and see that you have a lot of malware. You need to purchase our product to get rid of the malware!"
BF: "How are you monitoring my computer?"
Sc: "You have malware! We have your IP address!"
BF: "Well, can you tell me what my IP address is?"
Sc: "192.168.0.1 - you have malware!"
BF: *starts laughing uncontrollably*
Sc: "S-s-sir, you have malware! You need to purchase our product to save your computer! We are monitoring--"
BF: *continues laughing*
Sc: "Bu-but malware--"
BF: *hangs up phone*
You have mail.