Here’s what to do when you receive a “silent” scam call.
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ZDNET’s key takeaways
- There’s a reason scam callers don’t respond when you answer.
- The goal is simply to confirm that your number is active and spammable.
- To deal with a call, hang up and use spam filtering to block them.
Have you ever picked up your phone to answer a call from an unknown number, only for no one to reply? That “hello?” you’re shouting into the silent void could be feeding a machine. When you pick up a mystery call and hear nothing but dead air for three seconds, you aren’t waiting for a confused human. You’re actually waiting for automated dialer to hand you off to a live predator.
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Yes, there is a method behind the madness. Just knowing that someone answered the call is validation that the phone is owned by a real person and that the number is active. That marks the intended victim and number as available for future scams.
‘Automated reconnaissance’
“Calls where no one responds are rarely accidental,” Shane Barney, chief information security officer at cybersecurity provider Keeper Security, told ZDNET. “In many cases, they are automated reconnaissance events. Fraud operations run at industrial scale, and before they invest human effort in a target, they validate that a number is active and answered by a real person.”
What do scammers then do with your number?
“In modern fraud ecosystems, verified contact data has value,” Barney said. “It is bought, sold, and reused. A silent call can serve as a filtering mechanism, separating dormant numbers from reachable individuals. It is less about the conversation and more about confirming that there is someone on the other end.”
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In some cases, your confirmed number may lead to phishing calls or emails. In other instances, you might be the target of a more serious type of attack.
“Once that validation occurs, it strengthens the attacker’s ability to execute more convincing follow-on attacks,” Barney said. “A confirmed number can be paired with a breached email address, used to trigger password reset flows, or targeted for SIM swap fraud.”
These types of scams are nothing new, though they were more prevalent years ago, Barney explained. They seemed to go out of style as email and SMS phishing attacks became more common. Seeing them resurface highlights an important aspect of cybercrime. Attackers will reuse tactics and techniques that work.
What about calls in which the person responds after a short delay? That speaks to the automated operations run by spammers and scammers.
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“That pause is typically a function of predictive dialing infrastructure,” Barney said. “These systems place high volumes of calls simultaneously and use algorithms to detect when a human answers. Once a voice is detected, the system routes the call to a live operator. The delay reflects the handoff process. From an operational standpoint, this model allows scammers to maximize efficiency while minimizing labor costs.”
Is voice cloning a threat?
On the flip side, are you exposing yourself to any risks if you speak with the scammer, even just a few words? Voice cloning has always been a concern, especially with the advancements in AI. Could a scammer clone your voice and then use it to authorize purchases or run scams on your family and friends?
“Voice cloning is a real and evolving threat, but it’s important not to let it drift into science fiction,” Barney said. “Producing a convincing replica of someone’s voice typically requires a clear and sustained audio sample, not just a quick ‘hello.’ A brief exchange is unlikely to give an attacker everything they need.”
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Rather, risk comes into play when a cloned voice is used as part of a broader scam, Barney explained. If a scammer already has some of your personal details from public sources or data breaches, that cloned voice can add some credibility to the scam. That’s why you want to limit what you say to a scammer.
What to do next
With all this in mind, how should you handle these types of calls? Here are three tips.
Hang up. If it’s an unknown number and no one responds to your greeting, just hang up. The only downside here is that some calls with that initial silence may be legitimate, perhaps from an office, business, or known company. In that case, they will call back and can let the call go to voicemail. If it’s important, the person will leave a message.
Don’t respond, but stay on the line. Another strategy is to pick up a call from an unknown or suspicious number, but don’t say hello or anything else. If you hear nothing but silence, then just wait to see if the call disconnects. If the spammer or scammer doesn’t detect a voice on the other end, they may then consider your number inactive and remove it from their call list.
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Use spam call filtering. iPhones and Android phones do have built-in ways to block and identify spam calls. But a spam filtering app or service provides more granular control. In the US, the three major carriers — Verizon, AT&T, and T-Mobile — offer their own tools for dealing with spam calls. You’ll also find a variety of third-party spam filtering apps. Some apps to consider are RoboKiller, Truecaller, and Hiya.
But will these call filtering apps block you from all spammers and scammers?
The reality of call filtering
“Call filtering applications can significantly reduce the volume of nuisance calls, particularly those tied to large-scale spam campaigns,” Barney said. “They are especially good at identifying numbers that have already been reported and flagged by others, however, they are not perfect. Fraud infrastructure changes quickly, and new numbers appear constantly. A highly targeted call can still get through. These tools are helpful in managing volume, but they are not a substitute for sound security practices.”
To do their job, these apps also collect certain data from you, most notably your contact lists. Such information reveals who you speak with and how often. That’s why you should review the security and privacy permissions of each app to learn what data is collected and how it’s handled.
“There is a tradeoff,” Barney said. “Reducing spam exposure has clear benefits, but any application with deep visibility into your communications should be chosen deliberately. Filtering tools can reduce noise. Protecting accounts with strong authentication and unique credentials is what limits real damage if something slips through.”
