Did you verify whether it's the real McAfee Twitter account that is promoting this group?
Use something like the metacert browser plugin https://next.metacert.com/ in order to check this. If it's not the real Twitter account, then it's almost certainly a scam. Please double and triple-check your sources, guys

Be sure to check McAfee "John McAfee is charging $105,000 for tweets promoting ICOs" https://www.cnet.com/news/john-mcafee-is-charging-105000-for-tweets-promoting-icos/