Intelligent Solutions

Blocking fraudulent calls

Simon Woodhead

Simon Woodhead

26th September 2022

By Simon Woodhead

Ofcom publishes the ‘DNO list’, a list of inbound only phone numbers from high profile organisations that should never originate outbound calls. These numbers are highly desirable to scammers and frequently used in spoofing to defraud consumers.

Existing Ofcom rules can be interpreted to place a requirement on Public Electronic Communications Networks (which is basically anyone operating a telecoms platform, from a one-man band in a basement with FreeSwitch on a Raspberry Pi through to BT) to block calls on this list and any ambiguity will shortly be removed when Ofcom publish its much anticipated next Statement on CLI. That said, we know others have a somewhat laissez-faire attitude to rules such as this and as a result, fraudsters’ traffic can always find a home, to the detriment of the general public.

This blog is to let you know about a few changes we’ve made, and are making, as a result.

  • Outbound calls appearing ‘from’ DNO list numbers are blocked at network level (and thus for wholesale, Partner and Direct customers) as they have been for some time. However, we are now actively reporting on such breaches by wholesale customers and our compliance team is following up. As such, we are introducing an admin charge for handling such incidents which you’ll find in our ancillary rate sheet.  We’re not looking to catch anyone out here and whilst this charge is effective from October 1st, we will view first offences during October more leniently.
  • Wholesale customers who are unable to comply with the DNO list themselves directly may wish to delegate that responsibility to us. If so, we will do so with a simple agreement. Calls will be blocked for a simple monthly fee, avoiding any reporting above. Please speak to us if you’d like to put this in place.
  • We also see a moderately high level of incoming calls ‘from’ these numbers, attempting to defraud end-users, due to other networks allowing this traffic through. To protect end-users, we will shortly begin blocking inbound calls presenting these numbers in CLI. This is a no-cost no-opt-out service network-wide, for calls to both Simwood numbers and the many we host for other networks. It will apply to numbers ported into Simwood, but be dis-applied on Simwood or hosted numbers which have been ported out. Hopefully it’ll be a valuable enhancement for your customers.

Additionally, whilst we have long blocked outbound calls from invalid numbers, as a no-cost option, to ensure compliance with GC C6.6 in that context we’ve been unable to turn this same blocking on for inbound calls due to the volume of rubbish we were seeing from other carriers. Doing so would, in our opinion, have caused disruption and a support tsunami. 

<rant> Sadly support overhead and blame only ever flows down: if you can’t call a Simwood number from your mobile, that is apparently our fault; if you can’t call your mobile from Simwood, that is apparently also our fault. In fact, those often at fault are spared the support burden and it falls on those of us who’ve usually done nothing wrong but have accessible support! </rant>

Some years on, we feel we now need to and will be running a series of one hour trials over coming month. These will be announced on our Status Page. The intention is to turn this on permanently once we’re confident the disruption is minimal.

As always, our priority is to protect your end users and you from ever growing scrotitude. As we’ve signalled elsewhere though, your role is going to inevitably become more burdensome too going forward and we’re ready to help in any way we can.

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