Nicholas Weaver and Vern Paxson have published a paper estimating the worst case scenario of a network worm attack from USD$52 to $103 Billion. http://www.icir.org/vern/papers/worst-case-worm.WEIS04.pdf Although it was published last month, it was quoted in a new article today. One thing the left out the study was the improvement in productivity that occurs after you rebuild your Microsoft Windows computer. Some people regularly rebuild their Windows computer a few times a year. If companies and people have already factored in the need to regularly rebuild Windows computers in the Total Cost of Ownership, would a network worm really have that much additional economic impact? What's the economic impact of CTRL-ALT-DEL? The marketplace has already factored it in, because its business as usual. The well known (but not necessarily well respected) Mi2g Intelligence Unit has estimated the costs for previous infections as follows: Sobig: $37.1 billion MyDoom: $22.6 billion Klez: $19.8 billion Mimail: $11.5 billion Yaha: $11.5 billion Swen: $10.4 billion Love Bug: $8.8 billion Bugbear: $3.9 billion Dumaru: $3.8 billion SirCam: $3 billion