No DNS poisoning at Google (in case of trouble, blame the DNS)

[Stephane Bortzmeyer <bortzmeyer () nic fr>]

On Wed, Jun 27, 2012 at 03:53:17AM +0000,
 Matthew Black <Matthew.Black () csulb edu> wrote 
 a message of 18 lines which said:

> We believe the DNS servers used by Google's crawler have been poisoned.

[After reading the whole thread and discovering that Google was indeed
right.]

What made you think it can be a DNS cache poisoning (a very rare
event, despite what the media say) when there are many much more
realistic possibilities (<troll>specially for a Web site written in
PHP</troll>)?

What was the evidence pointing to a DNS problem?