Yahoo requesting GET vars that don't exist

It appears that slurp is auto-incrementing a get variable

[stargeek]

I've never seen this before but it appears that Slurp is spidering and indexing dynamic urls that don't exist like this:

page.php?IDnumber=1
page.php?IDnumber=2
page.php?IDnumber=3
page.php?IDnumber=4
page.php?IDnumber=5

and so on, these id's don't exist in the database and are never linked to from the site. They used to return blank pages, but we're making a fix to send a 404 on these pages.

has anyone seen this before?

PS neither google nor msn are doing this either.

[stargeek]

So no-one else has seen this auto incrementation spidering?

[Dijkgraaf]

I'd throw a 400 or a 410 rather than a 404, as most bots will re-request a page after getting a 404 on it previously.