Federal agencies are 'urgently investigating' whether the massive cellular outage that plagued Americans on Thursday was a cyberattack.

The Federal Federal Bureau of Investigation (FBI) and Department of Homeland Security (DHS) are on the hunt to track down what disrupted service AT&T, Verizon, T-Mobile and a dozen other cellular providers.

While the agencies have not shared details, a security expert told DailyMail.com that the outage has hallmarks of a hack.

Lee McKnight, associate professor at Syracuse University in New York, said the widespread nature appears to be 'a massive Distributed Denial of Service (DDOS) attack on core Internet infrastructure.'

This type of attack attempts to crash a website or online service by bombarding it with a torrent of superfluous requests at exactly the same time.

The surge of simple requests overload the servers, causing them to become overwhelmed and shut down.

McKnight, who is also an Affiliate of the Institute for National Security and Counterterrorism (INSTC), noted that DDOS is becoming a popular assault among cybercriminals.

He referenced the event in 2016, which saw the Mirai botnet bring down sites like Netflix, Twitter, Amazon and PayPal. 

'Some of those were launched by - kids for fun - others by malicious actors,' said McKnight.

'Reality is you cant rent DDOS as a service attacks by the hour on the Dark Web, so who exactly might be behind it may never by fully known/attributed.' 

The purpose of disrupting cellphone services could simply be to cause chaos, by preventing 911 calls.