This site uses cookies, if you continue you agree to our cookie policy.

Dial-Through Phone Fraud

This article examines the effect that dial-through fraud has on businesses and what steps can be taken to reduce this type of crime.

What steps would you take to protect your business from a burglar coming in after office hours and stealing £40,000? Would you make sure that all the doors have very good locks? Would you would install a burglar alarm and maybe even have CCTV surveillance? That should protect your business. Wrong! The burglar did not break into your office; they broke into your internal phone exchange (PBX). Unseen by human or electronic eyes, thousands of pounds are being spent on international telephone calls and your business will pay the bill.

How Does It Work?

Dial-through fraud is not a new problem, it just has limited publicity. It exploits a PBX feature that allows employees to ring in to the switchboard and, by keying certain dialling codes, make national and international calls for which the company will pay the bill.

Many businesses will take an "It will never happen to me" approach to dial-through fraud, even though most business PBXs are setup to be maintained remotely. This is to allow engineers from a maintenance company to make changes to the configuration without needing to make a site visit but it exposes the PBX. The administration port on the PBX will be connected to a modem that in turn is connected to an extension on the PBX.

Using trial and error, hackers will identify the number that this modem is on. The default passwords like "admin", "0000" or "1234" will be tried first. Even if the password has been changed, there are plenty of free utilities on the Internet that will use brute force to try every number and letter combination until the right password is found. It has been known for 16-character passcodes to be cracked in this way.

Once the hacker has gained administrative access to your PBX, they will identify unused extension numbers and set them up to allow dial-through using the company PSTN lines. For the cost of a local phone call, the hacker can be making calls to the Middle East, Far East, Africa, Australasia, etc. Some of these calls could be costing the business up to £3 a minute.

To compound the problem, the hacker will usually set up a disguised PBX that routes its calls through the company PBX. The hacker will then operate a "Call Sell"; selling international calls to customers at cheap rates. Alternatively they could make calls to their own premium-rate revenue-share services. It is possible that during the 15 hours when your office is closed, up to 10 simultaneous calls could be occurring. And that is just for one day! The problem is likely to go unnoticed and unresolved until the phone bill arrives at the end of the month.

It Will Never Happen To Me

A report in the Guardian highlighted the plight of one UK Company that suffered from a fraud attack. The company had secured its PBX with a 16-character password but it was still compromised. The discovery of the fraud was by pure chance when the MD of the company came into the office early one day to find the lights on the telephone switchboard lit up like a Christmas tree, even though he was the only one in the office.

The report showed that recovering the losses was not easy. Although the company's Telco admitted that the calls were fraudulent, it was not their responsibility to secure the customer's equipment from attack. Therefore the customer was liable for any calls made through the PBX. It was also discovered that the company's insurance policy had a standard clause exempting it from any "electronic losses".

There is also another example that uses VoIP to route calls into the country, where they are relayed onto the mobile phone network. Calls into the victim's PBX originate from a mobile number and are forwarded to international destinations by the PBX.

A Matter For The Police

Surely if a fraud has been perpetrated, then the police should investigate the matter? This is true. The Regulation of Investigatory Powers Act 2000 (Ripa) gives police the power to request "intercept data" from the Telco that would identify the origin of the inbound calls into the PBX. Under the act, a Telco is allowed to charge up to £1,500 to cover their costs of retrieving the data asked for by the police. This means that in every case, the police must decide whether the financial losses involved in the fraud justifies the cost of the "intercept data". For big losses, the answer is likely to be yes every time. However, in small cases involving just a few hundred or few thousand pounds, the answer may not be so clear cut.

How Can It Be Prevented

The most obvious way is not to allow remote access to the administration facilities of the PBX. However this may not be practical and could lead to increased charges from the maintenance company. The second method is to use a very random password on the PBX, up to the maximum number of characters, and to lock the modem so that it will only answer calls from a single phone number. This solution is very inflexible and after a while could be turned off if it becomes impractical.

A more comprehensive method is to invest in a Tracker remote node from Data Track. This can provide three key benefits:

  1. The Tracker can use secure access modems.
  2. By acting as an intermediary, the Tracker can offer different levels of access depending on the username and password given.
  3. The Tracker can proactively monitor the PBX looking for the first signs of fraudulent activity.

Tracker Secure Access Modems

The solution is hardware based; one modem is connected to the PBX, while one or more modems are deployed in the field. The Tracker modems use an encrypted secret key and a unique ID to provide a challenge/response to incoming calls. Consequently only a modem with a matching encrypted secret key, using an ID that is allowed by the PBX modem, will be able to connect.

This provides a more flexible alternative to calling from a single phone number. The modem is self contained and does not require any special software. It is unlikely that a random hacker using a standard modem will be able to breach this initial barrier.

Acting As An Intermediary

The Tracker solution is a gateway between the PBX and the user. It is capable of logging all log-in attempts. It can be configured to send out an alert (as an email for example) when it detects multiple log-in failures. This behavior would occur if a hacker was using a brute-force attack to try and discover the password.

Different combinations of usernames and passwords can be given different levels of access to the PBX. Users can be restricted to performing only certain actions from a limited menu choice. This prevents the hacker from gaining full unrestricted access to all of the administration functionality.

Proactively Monitoring For Dial Through Fraud

The Tracker solution can proactively monitor the call output from the PBX. It can be set to look for suspicious call activity. In the case of the company featured in the Guardian article, this would use a "rule set" to look for any call that occurred outside of office hours. When suspicious activity is detected, the Tracker would send out an alert containing the details. This allows an appropriate response to be taken, reducing the potential losses caused by the fraud.

Dial-through fraud can very quickly and silently cause thousands of pounds worth of losses to a business. The standard security precautions in place to prevent it are weak, especially compared to those used on IT networks. Trying to recover any loss is as difficult as detecting the fraud in the first instance. A Tracker solution from Data Track not only adds extra security to your PBX but a means of detecting losses before they progress too far.

By Dominic Martin