How to Prevent Bots from Spamming Your Sign Up Forms

Table of Contents

• What is a spambot?
• How to stop bots from filling out forms? Best ways
• Use a CAPTCHA
• Use a double opt-in form
• Add a test question to your form
• Add an unseen extra field or honey-pot
• Block Comment Spam
• Implement time-analysis
• Hide target request
• Form validation after geolocation of the IP address
• Use Web Application Firewall
• Blacklist IPs
• Limit IP addresses
• Beware of Cross-Site Request Forgery
• Spam signups can mess up your lists
• Protect your forms

Unfortunately, if you send or receive emails, gather email addresses or have anything to do with email at all, then you know about spam. Spam is a consistently frustrating issue, particularly for business owners and email marketers.

Table of contents

• What is a spambot?
• How to stop bots from filling out forms? Best ways
• Spam signups can mess up your lists
• Protect your forms

Likely you're interested in consistently gaining more subscribers or contacts to help your business grow. One way to do this effectively is to have a signup form on your website. If you don't have a form you should definitely make sure you add one for gathering information about people interested in your product or service. What you'll need to plan for, however, is that you're going to also get fake or spam signups as well. Possibly lots of them and these can really complicate your marketing campaigns.

Part of the challenge is keeping your forms protected in a way that doesn't get too complicated. So in result, regular users can still enter their information with relative ease. Here are some ways you can prevent bots or other spam sign-ups and keep your forms working properly for new contacts.

What is a spambot?

A spambot is a malicious program designed to gather email addresses and information from online sources like forms, chat rooms and websites. This information is usually collected in order to build lists for sending an unsolicited email - spam. Since emails have a distinctive format, it's easy to create such a bot. Sadly, it's much harder to avoid them. Some use address munging to confuse the bot by providing email in different formats, but it does have its downsides. That's why we got some fool-proof ways to prevent bots from spamming your forms!

How to stop bots from filling out forms? Best ways

Use a CAPTCHA

You've almost certainly already encountered a CAPTCHA. If you've had to try and interpret some distorted letters or numbers and submit them then you've filled out a CAPTCHA. You'll still find some forms that require this. Fortunately, this step has been simplified a lot to make it easier for humans. Basically, you're putting intelligent programming to allow people to check a box that confirms they are a living breathing person. This is easy for humans, but difficult for bots to do. You can implement this protective step for free, as this service is provided by reCAPTCHA.

Use a double opt-in form

In order to protect your form, you'll want to be using a double opt-in process for confirming sign-ups. This means that when someone enters an email address into your form, you're sending an automatic confirmation link to that email address. The user needs to go to their inbox, open the email and click the link. It will verify that their email is real and so are they. A bot is very unlikely to do this step. Any signups that don't complete this should not be added to your list.

Add a test question to your form

Elastic Email provides you with a double opt-in web form you can easily add to your website or landing pages for gathering new sign-ups. You have an option to customize this form in a variety of ways. This includes adding additional HTML which you'll copy and paste into your website page.

You may consider adding a simple question to the form that all humans will know the answer to but that will be difficult for bots.  Here is an example:

Email address:

A panda is black and

This way you know it's a bot if the input is not the word "white" and can delete the submission. Of course, you need to consider carefully the question you use. It needs to be something everyone will know in order to avoid any frustration for your potential subscribers.

Add an unseen extra field or honey-pot

A honey-pot in terms of form submissions means that you're setting up an extra field that bots will see and fill out, but that your real human users won't. It's basically behind the scenes filtering step that protects your forms. It doesn't add any additional steps for the real people trying to join your lists.

You can implement this by adding HTML and specifically styling it out using CSS. It's true that some sophisticated bots can now read CSS and Javascript. However, this is still an effective method and worth considering if you've got some basic programming skills. Here is a simple example:

CSS
.dispnon{display: none}

HTML

This gives you the basic idea. You'll want to make sure whatever field you've implemented as a honey-pot is not displayed on your actual form. If you get data that includes hidden information, you know it's a bot sign up. There are a variety of ways to do this and the code can be simple or more complex. An internet search can provide more examples if it's something you want to explore further.

Block Comment Spam

There are a few ways to specifically block comment spam and they can include changing the file names of standard URLs or moving your form pages from time to time. Another easy service to implement is Akismet. This service is designed to filter out comment spam and is implemented by using an API to activate their plugin.

Implement time-analysis

When you set up a form you should know that it takes a person around 3-5 seconds to fill it out. They need to type in their email address, their name and other information you have requested from them and click the button to confirm their subscription. The same can be applied to other various forms you implement on your page. The takeaway is that a human takes time to input all this data. However, bots are not constricted to the passing of time. They fill out the form instantly. 

It can be a great way to initially verify all the registered email addresses by monitoring the passage of time since a person clicked on a specific section or accessed the page with the form. You can also adjust the time depending on your personal needs. If you have more forms, how many fields are there to fill out. All this should be considered while setting up the time cut-off. There is a downside that you should take into consideration - the autocomplete option.

Many people use this option to automatically recognize and fill out the fields in a contact form without typing their details over and over again. Spending a long time to figure out the optimal amount of seconds to differentiate bots from a human can be a lot of work. It’s worth measuring the time from the moment users will click on the field up until they click “send”. You will be able to verify which ones are bots (that are instantly filling out the forms) and which ones are users with the autocomplete option. (Where it will still take around 2 seconds between clicking on the fields and clicking on the button.) Additionally, you can put a captcha that will require more time for a human to fill out the form.

Hide target request

One way of securing your contact forms from attacks is to not give the spammers the option to do it. Sensitive data like list IDs, account ID or form ID shouldn’t be available from the browser. Instead could be added from the backend side of it. The only thing your contact form will do is collect the information that the customer typed in and send it to your server. Then, you are able to fill out the actual sensitive data. It will trigger adding a contact to the list or sending a specific message. 

Anybody can attack from the customer’s browser angle, but not from your server since they have no access to it. 

Another way to secure yourself from spambots is to block the form once it’s filled out. Instead of allowing a person to sign up over and over again, allow them to sign up only once from a specific IP. Then, every time they access the page, instead of empty fields to fill out, they’ll receive a “you already signed up” message. This should only be used with newsletter signups though, as disabling the “contact us” form will just make it more difficult for you to maintain a good relationship with the customer. If they are blocked from asking questions, they will quickly move on to a different company.

Form validation after geolocation of the IP address

Similar to various sites blocking their content based on your location, you can disable the forms for certain locations with increased spambot activity. By monitoring their activity, you should be able to pinpoint the area that has the highest risk and block it. However, this can have a major negative side to it. If you block a certain location, you could ultimately stop the real users from the same location. Implement this solution only if you are sure that a certain area is generating significantly more problems than benefits.

Use Web Application Firewall

Web Application Firewall is a useful tool that can help you with XSS attacks and SQL injections. Now, this sounds foreign and scary but in reality, the concepts are pretty easy to understand. An XSS attack can inject malicious javascript or any other scripting code into a targeted browser and launch it. This can result in replacing the website content to make customers give up their data running a keylogger or stealing cookies.

An SQL Injection is very similar, although it injects an application in an SQL query instead. Then it can avoid authentication mechanisms, get unauthorized access to the whole database, read, create and launch files on the operating system it runs on and so on. The threat is very serious, and that’s why using WAF is so important. Usually, with free hosting or a shared server, this firewall will already be configured, but if you bought the hosting yourself, it’s your responsibility to set it up.

Blacklist IPs

If upon verification, you see suspicious activity coming from one IP address, you can blacklist it to ensure it will not send any more spam. Due to the nature of this method, it is kind of trial and error, where you first need to spot the spammer and then mark it.

Limit IP addresses

Set up a limit, for example, 10 forms, before blacklisting an IP address. With this, you can filter through the IP addresses and automatically block the ones that exceed the limit of available forms that can be sent during a specific timeframe. 

Beware of Cross-Site Request Forgery

Simply put, Cross-Site Request Forgery forces the affected browser to launch an unauthorized action. In this case, it’s an HTTP request that’s being forged or modified. This crafty attack damages the customer’s browser, not the server-side of the app. However, the server can see such requests as a perfectly legitimate communication with the browser. That’s why it is so important to protect yourself from it. Luckily, the solution is easier than you think. What you need to do is embed additional authentication data into the request, so the web application will be able to detect the unauthorized requests. There are a few ways to approach this.

A way of protecting yourself from this might be using Double Submit Cookies. It is done by sending a random value that is equally the same in an HTTP request and in a cookie. The server then checks if these values are equal. If they are not, it is recognized as a CSRF attempt.

Another option is using Anti-forgery tokens. They are typically random numbers that are stored in a cookie or on a server. What will happen is the server will compare the token attached to the incoming requests with the value stored in the cookie or the server. If the values are identical, the server will approve the request. Similarly, it will reject the request if the token is missing or is incorrect.

Finally, you can set up additional authentication for sensitive actions. This is a simple extra step when users perform such action. It prevents the attacks in case the user logs into a publicly accessible computer and forgets to log in as well as greatly minimizes the chances for a CSRF attack.

Spam signups can mess up your lists

If you're not currently convinced that it's important to prevent spambot signups or you're worried that adding an extra step to your form will stop people from adding their email to your contact lists, let's consider the alternative.

Not preventing (at least the majority) of spam signups can compromise the integrity of your entire email marketing program as a bulk email sender. When your list is comprised of a mix of legitimate and invalid email addresses, you're setting yourself up for a frustrating outcome the next time you send an email campaign.

Not only will you potentially damage your sender reputation by racking up a high invalid email count, but you'll make it harder for mail to reach the real people who actually wanted to get your messages. Recipient servers start to filter or reject mail from domains that send too many emails to bad addresses.

Protect your forms

Spam (sadly) is not going anywhere anytime soon. Take the time to implement one or more of these ideas and you'll save time and effort in the long run. A combination of different methods will be the most powerful, but even a single reCAPTACHA checkbox can help you prevent spambots without complicating your sign up process.

If you have any questions about your Elastic Email account, contact our friendly and fast Customer Success team!