For several minutes, McAfee’s Twitter account was urging his followers to buy up lesser-known cryptocurrencies. However, he later deleted the tweets and said someone had hacked into his account.

It isn’t totally clear how the breach occurred. But in addition to a password, McAfee’s Twitter account was secured with SMS-based two-factor authentication.

The extra authentication works like this: To access the account, you need both the password, and a secret code sent to your phone via text message.

All security experts suggest you enable the added protection. Even if a hacker learns your password, they still won’t be able to break into your account. Not unless they have access to your phone’s SMS messages too.

Well, that may have happened with McAfee. In an interview with the BBC, the 72-year-old claimed someone had intercepted his Twitter account’s two-factor authentication code. He first noticed the breach when he turned on his smartphone, and it showed an alert, saying: “SIM not provisioned MM#2.”

That alert suggests someone may have taken over McAfee’s mobile phone number, possibly by impersonating him at an AT&T store.

“I was on a boat at the time and could not go to my carrier (AT&T) to have the issue corrected,” McAfee told the BBC.

McAfee, a vocal supporter of cryptocurrencies, has more than 530,000 Twitter followers. Through his account, he’s offered investment advice and predicted that the value of Bitcoin will reach $1 million by the end of 2020.

Any tweet from his account could pump up the cryptocurrency market.

“Though I am a security expert, I have no control over Twitter’s security,” he said in a tweet after the breach. “I have haters. I am a target.”

But there’s also reason to be skeptical of the hack. McAfee is well known for his eccentric behavior and outlandish stunts. In the past, he’s run for US President and publicly lampooned the antivirus company he helped found. He’s also been arrested in Guatemala and fled Belize over his connection to a murder investigation

Ironically, one of McAfee’s most recent projects has been to develop a “hack-proof” phone.

Twitter so far hasn’t commented on the account breach. But the company has come up with a better option to the SMS-based two-factor authentication. It now supports third-party apps like Google Authenticator that can bypass the mobile carrier networks and generate a two-factor authentication code directly over the phone