It could be even more dangerous than you are imagining.

If you check a username, then you would probably also be revealing the IP address range and browser referrer that is normally used to access your account.

Google uses IP address and location to help detect illegal access. So giving away this information could make it easier for your account to be stolen.

How? Is the hacker going to buy a plane ticket, fly to my home and plug his laptop into my network?

Of course not. He's going to go botnet shopping and try to log in through a compromised machine with an IP address in the same town, in the same address range.

He might even be able to use the same IP as you, if you happen to be using a gateway with many machines behind it, and one of them is compromised.

"If you don't like to specify your full email address for any reason, you can replace up to 3 characters with asterisk sign (e.g., for [email protected] enter myac*[email protected]), thus we'll show you a count of matches for this pattern. We respect your privacy."

Only up to 3 characters? Why 3? Especially since it's an email address and not a random string, which limits the possibilities for the 3 missing characters. This looks like it's giving more info than you'd think to a dodgy website...

maybe because they want to limit the search time?

Exactly. just show me the list and let me do a command+f. I'm not trying to enter my email into their system.

Are you being serious? Next time you search google, would you rather they display 5,000,000 results on one page and you Ctrl+F the response?

Wget and grep would be more likely to be used - but in answer to your question: yes, in a case like this.

Let's do some quick back-of-the-envelope math. 5M addresses, with very few longer than 25 characters. Let's say the average is around 17 characters. 17 * 5 * 10^6 = 35 * 10 ^7 = 3.5 * 10^8 bytes, or 350MB. Text generally compresses to 1/8 space with zlib, so the amount to transfer would be about 44MB, at most. Serving the list as xz compressed file could probably cut the size down to below 40MB.

In the age of 100MB youtube videos, that doesn't sound like much to me.

If the local client could handle it, this would be a much more secure way of browsing.

i sure hope you are beeing sarcastic, if not, consider this: it is possible to use javascript to override ctrl+f or other keystrokes. if that site would have displayed the list, and someone used ctrl+f on it, they could have simply used such a technique to add your input to the list to generate positive findings on the fly.

http://arstechnica.com/security/2012/12/how-script-kiddies-c...

you should reconsider this, because it is possible to use javascript to override ctrl+f or other keystrokes. if that site would have displayed the list, and someone used ctrl+f on it, they could have simply used such a technique to add your input to the list to generate positive findings on the fly.

http://arstechnica.com/security/2012/12/how-script-kiddies-c...

To avoid this, I made this script to check if my email addresses are in a leak list: https://github.com/rodrigorega/wordlist_compare

nice.. i'll use grep instead, thanks for the effort though

Give me your email, and I'll check for you. I won't do anything, I promise. Joking aside, I downloaded the list and my email is not listed. Phew...

I also checked a few of those near and dear to me. Should probably try my full address list...

...or that when you log on to the site, the site would tell you that your account was in the list.