How Easily Can Hackers Plant Evidence?

Earlier this week on The Atlantic, security expert Bruce Schneier took stock of our collective anxieties in the wake of the Ashley Madison hack. Is our online activity ever really private? A reader takes that worry a step further:

In a non-material realm where all data can be fabricated and easily transferred, what’s to prevent hackers from framing people?

The example I keep returning to is Internet child porn. In the case of criminal offenses like that, the presumption of innocence tends to get hindered from the outset by the severity of the charge. The mere accusation is enough to put someone under a cloud of suspicion, or to impeach their credibility. And it seems to me that anyone who can hack a computer network can also compromise someone's home computer to plant files on it.