iPhone users have been unsettled by blank emails apparently sent in 1970 appearing on their phones.
The unusual iOS bug causes phantom emails to pop up in the phone's native email app, with no sender, subject or content and a date of 1 January, 1970.
The strange glitch has been widely reported recently, but it's been a known iPhone issue for a while - phantom emails have been making appearances in users' inboxes since June 2011, based on reports from social media.
UNIX time is used by computers to make sense of times and dates, and takes the form of a number showing the seconds since midnight on 1 January, 1970.
At the time of writing, the UNIX timestamp is 1457459002, because it's 1,457,459,002 seconds since that particular time.
When the email app fails to receive the time data properly, it defaults to 0, explaining the unsual dates on the messages.
Of course, even if it was possible to email people in the future, there wouldn't be any from 1970 - Ray Tomlinson, the inventor of email, only sent the first one a year later, in 1971.