Comment #6 on issue 20306 by [email protected]: SafeBrowsing flags sites  
that only include images (even 404s)
http://code.google.com/p/chromium/issues/detail?id=20306

The blacklist is at different levels of granularity. We do have the  
capability to
blacklist a single file on a host, e.g. one image on an image site. We also  
have the
capability to list an entire host, this usually happens when we find a  
significant
number of the pages on the site to be compromised (often a rampant sql  
injection
attack, or a compromised web server, e.g. someone modifying the apache
configuration).

So, yes, there is a possibility of false negatives, but I think you are  
overstating
the likelihood. If someone includes an image from a site where the entire  
site is
listed (e.g. a.com is a forum, b.com is a site where the majority of pages  
are bad so
we list all of b.com, and a user includes an image from b.com on a.com),  
then from
our perspective b.com is so compromised we don't want to trust any of the  
resources
on there.

You make the assumption that we can't block a major free image host. While  
it is
correct that we would likely not want to block the entire thing, we can  
block
individual files on the host.

"Why don't you at least just block the specific image from loading" -- in  
general,
it's a much harder problem than this. Abstracted one level, what we see is  
the
following. There is a page, that page includes something bad. We know our  
list
doesn't have 100% coverage, and we know that the page has some  
vulnerability that
lets bad things be included. (That vulnerability could be by design, e.g.  
allowing
users to post images, it could be something like sql injection, etc, from  
the browser
pespective we have no idea.) So, we could not load the known bad thing, but  
we would
not want to tell the user "hey, it's safe to go here cause we blocked the  
bad stuff"
-- we know we don't have 100% coverage, we know that there is a  
vulnerability on the
page and that that vulnerability has been exploited, so instead we tell the  
user "you
should not go here." We actually see a lot of cases where there's a webpage  
that gets
hacked, and scripts and iframes are added to multiple different hosts, some  
of which
are on the list and some are not. So, we wouldn't want to just say "Well,  
we blocked
the ones we know about, you're safe now."

It's really not an easy problem :(

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