Silent phone calls might lose you money, Information Security Authority warns

On Feb. 24 the Ministry of Information and Communications’ Authority of Information Security said it received many reports about people getting calls from unknown numbers with the caller hanging up immediately or remaining silent.

"This could be due to a technical error, but it could also be a ‘bait call’ to rouse people’s curiosity and make them call back," the agency warned. If it turns out to be the latter, callers may be hit with high phone bills even without anyone replying.

Its experts said this sort of spam used to be common in the U.S. and Europe last decade and is now resurfacing in Vietnam. The spammers usually use a certain device to automatically make calls on a large scale – to hundreds of millions of random phone numbers across the globe – to capitalize on people’s predilection to return missed calls, they explained.

As communication via phone becomes increasingly common, particularly with online shoppers not wanting to miss delivery people calling from unknown numbers, people could unknowingly become victims of this spam, they said. "Not only do users get annoyed and confused, but they also lose money in their phone account because of this spam."

People may become unknowing spam targets from silent phone calls. Photo by Pexels

The spammers use fake phone number prefixes to give the appearance they are calling from domestic phone numbers to mislead people into thinking can call back on the cheap, but in fact users could be making calls that cost tens or hundreds of times more per minute, they added.

A security expert pointed out that charges to a foreign landline could be very expensive with some calls even charged when the phone merely rings. The authority said: "Most of the spammers’ phone numbers are hard to detect since they resemble the phone area codes of some regions in Vietnam."

Experts warn that scams through social media and the internet are becoming more and more sophisticated, and also expanding to phone calls with unpredictable outcomes.

The authority warned: "If you receive a call from a number which does not seem like a regular landline or mobile phone number, or which is not affiliated to any known organization, exercise the utmost caution, and do not pick up or comply with directions from these unknown persons."