Mariann Hardey’s father died unexpectedly a little over a decade ago. But he lives on through his Twitter account. It only has 42 followers, and it was locked by Hardey’s father so no one but those 42 people can see it. And with a common first name and surname-based username, it’s likely a sought-after bit of online real estate.

“I regularly check in with him over social media,” says Hardey, a sociology professor at Durham Business School in the UK. The profile—the last tweet of which praised Hardey for her braveness in getting a…