How to Block Teams Call-01

How To Block Calls In Microsoft Teams

Table of Contents

Spam calls, cold calls, scam calls are all on the rise and even more so with the explosion of cloud based telephone systems available. It can severly disrupt work and also encourage anxiety with the victim. In this article, we discuss how to block calls in Microsoft Teams.

How big is the problem? – It’s huge!

In the summer of 2021, Ofcom estimated that in the three months of summer approximately 44.6 million scam phone calls or texts targeted UK residents. A recent 2022 Google data review now estimates this number to be at least 34% higher.

Most of these scam / spam calls target consumer phones, but as the boundary between work and personal information gets more and more diluted, these calls can make their way into the enterprise. IT Admins now find themselves fighting a growing battle to keep users and data safe against such attacks.

Identifying a Spam / Scam Call

Scam and Spam calls vary in their complexity and believability. It is not always immediately obvious that a call may not be genuine. These types of calls increase in frequency around a legitimate event happening in public.

HMRC tax scams usually increase in January because this is when HMRC require self assessment tax returns to be filed. Medical scams, like the fake COVID vaccination certificate centre to continue with the example.

But not all are so ‘mass market’. Some are highly personalised and targeted and the caller can sound convincing when playing back known facts about you. “I see you have just bought a washing machine from Currys”. Or “Good evening Sir, I am Adam calling from HSBC. We’ve detected some potential fraud activity on your account and are calling to confirm these transactions with you”.

They are designed to catch the victim by suprise and provide enough credible cause for the victim to ignore their hestiancy and engage.

Fortunately there are some guiding principles that you can employ to ensure that you do not fall victim to one of these scam calls.

5 Simple Tips to Spot a Scam Call

  1. Look at your caller display. Is the number withheld? – If yes, this is probably not a legitimate call. Hang up and call the company back using a phone number found on their website. If the call was genuine, there would be a record of the call being made on their systems. If not, you probably avoided a scam call.
  2. Look at your caller display. Does the number look legitimate? – Most smartphones will lookup the caller’s ID against a phone directory and return the name of the business. Android uses Google business directory. In the USA, there is a central database carriers subscribe to called CNAM. If it doesn’t return a name, it doesn’t necessarily mean it is not legitimate but you can look at the number and spot if it could be faked. Fake numbers (Spoofing) can sometimes be easy to spot as they will contain consecutive uses of the same number or repetitions of the same 2 or 3 numbers e.g. 01121112223.
  3. How long does it take for the caller to answer? – This is another giveaway. If you answer the call and it takes more than a second for the caller to be connected to you, then this is most probably a spam or scam call. It is a sign that the caller is using an auto-dialer / robodial and just waiting for the first person in their dial block to answer. Just hang up if you suspect this.
  4. Requesting to Validate Your Account Immediately – If you do answer, if the caller introduces themselves and then immediately asks you to confirm your account details with them without giving you a good reason for the purpose of the call, then it is most likely a scam call. Hang up or explain that you are not comfortable passing this information and that you’ll call them back using the customer support number found on the website (especially if it is your bank).
  5. Automated Answering Messages – When you answer you are played an automated message that is pretending to be human “Hello… I’m calling because you’ve not paid your bill. Is that right?!?” – Some can be particularly threatening. No legitimate company or organisation is ever going to adopt these systems. Hang up. Do not press any button and do not call back.

How Can I Block Scam Calls In Microsoft Teams?

There are a number of protections available within Microsoft Teams that can help reduce and block scam calls. Some are admin controlled while others are within each individual user’s realm of control. We will go through each setting to ensure that you are as protected as you can be.

Spam Filtering in Microsoft Teams

The first is spam filtering. Spam filtering has been available within Teams for about 12 months and uses Microsoft’s own algorithms and data to determine a spam score for the incoming call. If this feature detects the call is suspicious, it will header the call toast with ‘Spam Likely’ allowing the recipient the chance of declining a potential scam.

Microsoft Teams Spam Call Detection
Spam Call Detection in Microsoft Teams

This feature is turned on by default using the Global Calling Policy in Microsoft Teams. However, for user assigned policies, the Teams Administrator may need to alter it.

Turn on Spam Filtering in Microsoft Teams
Spam Filtering setting in Microsoft Teams Calling Policy

This setting has three options:

  1. Enabled – When set, filtering is fully enabled. Both basic and captcha interactive voice response checks are performed.
  2. Enabled Without IVR – Only basic checks are performed. A call may get dropped if the spam score is high
  3. Disabled – Spam filtering is turned off

Block Callers With No Caller ID

This feature is enabled by default on all Microsoft Teams clients. The user has the ability under their privacy controls to block callers that do not have a Caller ID displayed.

Block Calls with no caller ID in Microsoft Teams
Blocking Anonymous Callers in Microsoft Teams

Enable this by clicking on manage account in your Teams client (located by clicking on your profile image) and choose the Privacy tab. From there, enable the checkbox to block calls with no caller ID.

Personal Call Blocking

Personal call blocking in Teams allows any user to decide if a caller should be blocked from reaching them if they attempt to call again. Whilst this feature prevents subsequent calls, it does require the user to have to answer the first (or a few) calls and be subjected to the potential scam / spam call in the first place.

A user can do this from the Calling app within their Teams client and hovering over the call in their history. Click on the elypsis (…) that appears and select block from the dropdown.

How to block a call in Microsoft Teams
Blocking a Caller in Microsoft Teams

It is only possible to block phone numbers in Teams. You cannot block Teams to Teams calls using this method. For more information about this, see information barriers.

To unblock a number in the future, go to manage account > Privacy > Managed Blocked Contacts and unblock the number you wish.

Unblock a number using Microsoft Teams
Ublock a number using Microsoft Teams

Tenant Wide Call Blocking

Microsoft Calling Plans, Direct Routing and Operator Connect all support blocking of inbound calls from the PSTN. This feature checks the Caller ID of every incoming PSTN call against an administrator controlled list. If a match is found, the call is rejected before being routed to the intended recipient.

This feature is useful for particularly repeat offenders who are targeting a wide range of users internally. At the moment, the only way in which an admin can manage the list is using the Teams PowerShell Module.

When creating the block list, the order in which you create the blocked entries is not important. The first rule that matches will result in a block. The experience to the caller may differ depending on the carrier used from a graceful message to a call drop.

Block A Number Using Microsoft Teams

Admins can block an individual number using a literal pattern or a range of numbers using regular expressions.

Blocking an Individual Number:

New-CsInboundBlockedNumberPattern -Name "BlockNumber826236" -Enabled $True -Description "Block Ewan Haig" -Pattern "^\+?441235826236$"

Blocking a Number Range:

New-CsInboundBlockedNumberPattern -Name "BlockRange" -Enabled $True -Description "Block Callroute" -Pattern "^\+?44123582\d{4}$"

Allow a Number

To allow a number, all you need to do is remove the block rule that is affecting it. Where you want to permit a single number within a range will require the removal of the blanket block rule and the creation of two new rules to block all numbers within the range before the allowed number and another for all the numbers after the allowed number.

Remove-CsInboundBlockedNumberPattern -Identity "BlockNumber"

View The Block List

To view a list of blocked numbers, use the following PowerShell command

Get-CsInboundBlockedNumberPattern

Summary

In summary Microsoft Teams has a suite of tools that can help to reduce the impact and frequency of scam calls and when implemented properly, can be quite effective.

However, users will still need to employ a degree of caution when receiving unsolicited calls as scams adapt, numbers may change to bypass these controls.

If users suspect a scam call, they should immediately protect themselves from further targeting by blocking the number in their Teams client. They should then raise an IT Ticket to inform of the suspected phone call and then IT should make the decision to enforce a tenant wide block on that number to protect other colleagues from falling victim.

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