If I'm reading their summary right it looks like a big piece of that spike might have been the botnets trying to re-establish themselves. (Quoted from your link just to show what I'm looking at): "Zombie activity also dropped significantly after Rustock was taken down, but large increases of enslaved computers became evident following the malware outbreak at the end of the quarter."

Does anybody know what a "Parked domain" is?  I'm wondering what they're referring to when they say this: "Parked domains were the website category most likely to contain malware."

Interesting read.  Sure is a lot of spam out there.

Generally speaking, an unused domain which just goes to advertisements/links.

Ah, thanks.

My understanding was the same as DaveRI's.  It was not surprising, but still sad.  I wonder how many computers were re-infected by "Aunt Ida" clicking on those attachments/links in the emails?

Most likely far too many I'm afraid. People are fond of receiving stuff in their emails. I know I was when I first got into this. I know better now.