Did Malcom Young, the guitarist and co-founder of the band AC/DC, pass away? Yes he did... in 2017. News of his death went viral again in 2018 around the one-year anniversary of his passing. He is indeed dead but it is old news.
The story being shared around widely again is an article published on November 18, 2017 titled "Malcolm Young, AC/DC Guitarist and Co-Founder, Dead at 64" (archived here) which opened:
Musician who co-founded Australian rock legends in 1973 with brother Angus Young dies following battle with dementia
Users on social media only saw this title, description and thumbnail so they would not have seen any indication it happened last year:
Malcolm Young, AC/DC Guitarist and Co-Founder, Dead at 64
Musician who co-founded Australian rock legends in 1973 with brother Angus Young dies following battle with dementia
Here are some people sharing the news as if it was something that happened recently: