Be prepared if you have a kid: New way to explain that old question...

CHILD:  Dad, where did I come from?

DAD:  Okay, we had to have this conversation some day!

Listen, Son.... Dad and Mom met in a chat room on the net. I set up a meeting with your mom and we landed in the bathroom at the Cyber Cafe.
Then, Mom did some downloads from Dad's memory stick and when Dad was ready to upload, we discovered that there was no firewall.
Seeing that it was a bit too late to cancel, Dad just carried on doing the upload.
Nine months later, the damn virus appeared!

CHILD:  Huh?