Dio has been suffering from stomach cancer for a while now and this was said to be why he passed away.
After a few hours of the rumors circulating, Dio's wife/manager dispelled the rumors and confirmed he is still alive but not well.
"I am at the hospital and Ronnie has NOT passed away!!!! He is not doing good, but he is not dead. I will let you know if anything changes. Thank you for your concern."
You can see when people went into panic mode...
before I took that screen cap the hotness was Volcanic