To 'hack' is to make violent and fairly crude chopping movements, like cutting down a tree with rough axe. 'Hacked to death' means that this person was attacked in this way until they were dead. It's the same construction as 'beaten to death' or 'starved to death' or 'burnt to death' : it simply describes the means by which the person dies.

SuKi is right for general usage. Here, it's possible that "hacked" is being used in the sense of destroying computer-related files, since the subject is a blogger. It could mean that the blogger was forced to stop writing because of hackers attacking his computer.

hack something to something to cut something up into something roughly or crudely, such as pieces, bits, smithereens examples: The editor hacked my story to smithereens. Don't hack the turkey to pieces!