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   Re: [xml-dev] Can A Web Site Be Reliably Defended Against DoS Attacks?

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Dare Obasanjo wrote:

>That solution basically amounts to creating a user hostile system where users can't run applications unless allowed to by the system administrator. As for the home user, I don't see how this ultra-cumbersome approach would even get off the ground let alone fly with the average IMing, music downloading teenager. Even if you did all that they'd just go through all the steps and launch the application. 
>How many people would have believed that requiring a user to download a zip file, unzip it's contents then launch the contained executable would be a virus vector that would actually work let alone be one of the fastest spreading of all time? 
We had an interesting experience here last week, related to viruses.

Just by storing a particular unfortunate file onto our server, it
froze Windows Explorer sessions across the PC network for people
accessing that directory. Well, froze for 2-3 minutes 
every time anyone clicked or dragged-and-dropped etc. the file.

This was a new thing to me: a file being a kind of DoS just by
being placed in a directory and not even executed. 

We finally traced the problem back to Norton anti-virus 2003 on
the PC clients, which were acting as advertised unfortunately. 
The file, you see, was a .exe of a self-installer; Norton saw 
that the .exe had compressed contents and would try to uncompress 
and scan the contents each time almost any operation was attempted
(uncompressing and scanning a 30Meg file seems slow over a network,
presumably it requested a small chunk at a time so there was
a lot of latency.) While NAV was doing its stuff, the Windows
GUI was frozen. The problem could be fixed by turning off
NAV, or removing the file from the server.

(We went back to the maker's of the self-installer program,
Tarma, and they responded with a fix within 2 hours to 
avoid the compression that triggered NAV. Excellent service.)

What a state we have arrived at, when operating system
need anti-virus software which can cause this kind of headache.

Rick Jelliffe


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