Customers were left in the dark for nearly 12 hours after they were stuck on SOS mode from 9:30am ET until 7:30pm ET.

While Verizon has not revealed the cause, experts told DailyMail.com that a cyberattack by Russia or China 'is plausible.'

The CEO of a leading global cybersecurity firm explained that hackers could've prompted Verizon's online routers to release a malicious signal to cell towers, disrupting communications for thousands of people.

Kyle Hanslovan, the CEO of Huntress - a leading global cybersecurity firm told DailyMail.com: 'This could be a call to action that if the [Verizon outage] was a hijacking, what are companies doing to prevent these kinds of attacks from happening.'

Hanslovan noted that 'it isn't clear whether the Verizon Wireless outage is the result of a mistake or something more nefarious,' adding: 'However, the likelihood this was a purposeful cyberattack seems just as plausible.' 

At least 100,000 people were impacted by the Verizon outage, with customers living in the Midwest including Illinois, Wisconsin and Indiana being hardest hit. 

Mobile phones switched to SOS mode, limiting communications to only emergency calls.   

Verizon hasn't confirmed what caused yesterday's outage, but Dave Hatter, the director of business growth at Intrust IT told DailyMail.com: 'The fact that Verizon has not indicated what cause the problem or how they will ensure that it will not happen again has caused some to speculate that it could be a cyberattack. 

'That said, they may be tight lipped about it to ensure that information that could lead to a cyberattack is not released.'

The Federal Bureau of Investigation (FBI) has warned that cybercriminals in countries like China target critical infrastructure to 'physically wreak havoc' or disrupt services at any time they choose.