Is Google spidering URLs which appear in email?

[doc_z]

I have an alert service where users can create custom news alerts. In this process unique URLs (which contain a hash value) for verification and deletion are created.

Now I'm seeing one of these URLs "id=...&hash=" in Google's index but not in bing's or Yahoo's index. I'm not not Adsense or any other kind of advertising on the page. I'm not using Google analytics.

I'm just seeing two possibilities how Google has found that URL: either is was due to the bowser/toolbar or identifying them in the e-mail (of a Gmail account). Unfortunately the entry in the database which belongs to that id is already deleted. Therefore, I doesn't know if it was a Gmail account or not.

Has anybody else seen a similar behaviour?

[tedster]

Over the years there have been several posts suspecting this. But as you say, if someone with a toolbar installed clicks on that email URL, that could trigger the crawl, too. Seems more likely.

[walkman]

Toolbar could be it, I know that because of my password protected admin pages.

Gmail is a possibility too