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If I display my email address on my website, I would probably receive a lot of spam, so I can set up a contact form instead. If I want to display my phone number, how can I prevent unwanted phone calls?

Anders
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Grafica
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    You can trust the internet to be kind and not abuse your good intentions. –  Jan 02 '13 at 02:23
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    If you feel you can't trust then purchase a sip configuration file and setup your own voip server using asterisk for example. You could then do a redirect with some voip antispam feature to avoid abuse. Sip configuration file cost about 50$ CAN and an asterisk server can run on a 20$ pentium 4 machine. If you wish to get a better encoding you can do so by purchasing a encoding licence to Digium. Those kind of config run smoothly even using 3g vpn as when setup properly the encoding can works great at as low as 100 kb/s. In other words, it could run over 3g in the back of your trunk lol – happy Jan 02 '13 at 02:35

7 Answers7

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Well, the first thing is not to worry about it so much, because your threat model is unlikely.

Voice spammers don't get phone numbers by sending bots out to crawl the web, because they have much better sources of numbers.

And targeted attacks, where someone wants to prank call you specifically, can't be prevented because you can't tell who is an attacker and who is a customer.

If you still want to obscure your text, then here you can use similar techniques to those used to obscure email addresses:

  • Do the formatting weird so bots don't recognise it as a phone number.
  • Use an image of the number instead of the text. (But please don't do this, because it'll break accessibility.)
  • Shrug your shoulders and put good anti-spam in place.
Graham Hill
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    +1 on this. You have no idea how often companies keep copies of the Experian credit database on USB sticks and the like. I can download a year-old copy of the UK one right now from a torrent, and it'd have ~20m home phone numbers in it, along with names and addresses. – Polynomial Jan 02 '13 at 13:01
  • I tend to make info like emails or phone numbers be displayed by javascript, after a short delay or click on the field. – Sebi Mar 22 '16 at 21:20
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    Voice spammers don't get phone numbers by sending bots out to crawl the web, because they have much better sources of numbers. @GrahamHill Can you give an example for that? – uuu May 06 '16 at 09:07
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    @toogley any of the multitudes of online phonebook websites, or millions-scale data leaks? – Οurous Apr 27 '17 at 14:43
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    The claim about voicespammers isn't true. The voicespammers buy their numbers from people who scrape the numbers. I set up a separate phone number specific to a service offered on a site and once the number was added to the page it began to receive bogus calls. – Aunt Jemima Sep 13 '21 at 14:10
  • Voice (or text) spammers obviously DO use data scraped out of the Internet to built personal information databases for selling them on the dark market. Maybe they do not always blindly crawl the web (some do, though), but they definitely scrape some websites (either targeted or not). @Ourous, how do you think the databases sold online are built ? Data from leaks is a tiny small percentage of all the info available on the dark market and phonebook websites are most likely outdated and negligible (we are not in 20th century anymore). This was already true in 2013, even more in 2017 – cedbeu Nov 27 '23 at 05:29
  • 1 day after displaying the phone number on my site I got a call from Monaco... – inf3rno Mar 28 '24 at 19:31
4

If you are in the US or Canada, you could use Google Voice (or any other VOIP service) and supply the Google Voice number. Google has pretty good anti-spam features built in to Voice and you can block any numbers that are problematic or only allow it to forward to your phone at certain hours.

AJ Henderson
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Google Voice gives you, for free, an alternate phone number that you can (selectively) forward to other numbers. They also have a widget you can embed onto a webpage that can be used to call you directly from the page.

tylerl
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  • The widget was a great idea; unfortunately it appears to be unsupported as of 2019. I had one on my website for many years and sometime recently it stopped working without any notification to me (sends back a 403 when submitted). I can no longer find an option to embed it. – Soren Bjornstad Jul 13 '19 at 23:27
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Not to be credited for. This is the source

HTML

<p><span class="rev email">emos</span></p>
<p><span class="rev phone">321</span></p>

CSS

span.rev { unicode-bidi:bidi-override; direction:rtl }
span.rev.email:before { content:"moc.etisbew" }
span.rev.email:after { content:"@nhoj :liamE" }
span.rev.phone:before { content:"987 654 " }
span.rev.phone:after { content:" 153+ :enohP" }

which will result in this

Result

cybernet2u
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You can use the same methods that are used for e-mail adresses:

  • Replace with image (bad for accessibility)
  • Encode in some weird way (e.g. ROT13+Base64) and decode using JavaScript (prevents bots that cannot execute JS from reading it)
  • Require ReCaptcha to show (inconvenient)
  • Make hard to detect by inserting hidden text between the individual numbers

In addition to this, you can replace zeros with uppercase o's, however some scrapers can handle this (note that the scrapers I'm talking about are not used by spammers).

Honestly, I doubt phone spammers scrape web sites for numbers, much easier to simply dial all numbers and detect which ones exist.

Jan Schejbal
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0

create class in css id='hide' and set it to display=None;

then use this class in html as follows:

01482 <span id = 'hide'> 548asd46</span> 564654

this splits the number but hides what shouldnt be there

lucy
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Another Possible Solution (?)

<iframe srcdoc="(NNN)NNN-NNNN"></iframe>

Depending on whether or not the bot will scrape the contentDocument of an <iframe> -- AND -- if that iframe is visible from "view page source", this may also be an option. I'd be interested to hear the thoughts of someone more versed in security than myself.

Cody
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