How to Smell Difference Between Humans & Robots - Annoying Captcha Forms

I notice that most people implementing CAPTCHA don't even fully realize what they're protecting from.

There are different kinds of spam, each needs a different approach:

1. targetted attack against a site

2. non-targetted attack sending spam for machines

3. non-targetted attack sending spam for humans

To protect against first case (e.g. someone trying to mass-register webmail accounts) you have to have a proper CAPTCHA, and JavaScript tricks and hidden fields are totally useless.

Most sites are only spammed with second type of spam, but choose protection against the first type! However, this spam is super-easy to defeat with content classification, because it has to make spammy keywords/links available to machines.

The third one is common in e-mail, rare on websites, but still can be mostly defeated with blacklists, classification and technical tricks that catch poorly written bots.

There are people implementing protection against #1, and then trying to prove it works, because it blocks #2 and #3. In non-targetted attacks, anything that wasn't expected by the bot writer will work, even if it's totally misimplemented CAPTCHA that has solution in image's URL, or it's a choose-a-kitten test that has 1 in 9 chance of guessing, or mouse movement tracking that can be trivially simulated/replayed.

recaptcha didn't originate at Google. There are smart people working outside the Google and Microsoft ecosystems. While I am not a real fan of Stack Overflow, they've had incredibly nebulous questions that have turned into wiki's before - this one somehow failed to meet their standards.

First thing in a startup - solve someone's pain. Human Verification is a pain point for web data entry.

At least he's trying to solve a problem he faces. Imagine if he took a heatmap of all mouse movements during form submissions, ranked them as spam/ham, and then used that heatmap against new submissions to determine a confidence. Perhaps there is a pattern. It's difficult to know the answer to a question that isn't asked. Maybe during data entry, your analysis returns a fact that in human submissions, they press backspace at least once.

Sure it doesn't work for mobile browsers/touchscreens, but, on low-confidence submissions, you present a harder, second challenge.

Most recaptcha forms are solved by humans at $1/1000 from companies. You have caused them to use a human to solve it, which means your test worked. The fact that you still got a spam submission is a separate issue.

Ensuring a human, non-spam response is something that needs to be done statistically, not through a rules based system. Shared inoculation like Akismet or Typepad help, but, often miss new trends.

I don't think the real problem is determining if it is a human, I think the real problem is dealing with the contents of the form submission. I could care less if the form is automatically submitted, as long as I know whether to ignore that form. Captcha just erects a small barrier.

One of the best things I ever did to combat spam on inbound mail was greylisting + dspam + tmda. If dspam has a high confidence that it is spam, tmda sends a challenge/response. While I've never given out my gmail address, the amount of spam it receives is ridiculous. My own solution, even the spam folder rarely sees more than a few messages a week. My personal blog, discounting trackback spam has had 71 spam posts in the last week. I use RPXnow (requires one of the shared auth providers or someone needs to create an account) and recaptcha with Akismet. It hasn't stopped the spam that is received, merely what gets automatically published. I do believe that every submission received on my blog comes from a human, or has at least had some human interaction. Captcha doesn't solve the problem, merely erects a small barrier and just makes sure the spam I get is more likely hand delivered.

I suppose it depends on the application. For signup spam, the expected return is definitely higher than the current cost. And unfortunately, it's also on a website's critical path, so making signing up more annoying is strongly against the best interests of a company.

In other words, it's a pretty hard problem.