Buzzfeed has found that videos sent via smartphone app Snapchat - which should disappear after a few seconds - can be preserved and reviewed.
Snapchat has proved popular as it deletes sensitive or risque photos and videos after a short delay.
Snapchat said such "reverse engineering" was always going to be possible.
Using a widely available file-browsing computer programme Katie Notopoulos, a staff reporter at Buzzfeed, found that Snapchat and its Facebook equivalent Poke kept copies of videos that should be deleted. The ability to send video via Snapchat was introduced on December 14, the BBC reported.
When videos were loaded but not opened, it was possible to get at and view these copies when users connected their iPhone to a computer and used a file browser to look through its internal memory, Notopoulos discovered.
If videos were not viewed, she found, they were stored in a folder called "tmp" by Snapchat or "mediacard" on Facebook's Poke. Copying the files in these folders to a hard drive stopped them being automatically deleted.
Snapchat is also available on Google Android phones. Notopoulos did not try to find out if videos were preserved in the same way on such smartphones.
However, earlier in December Snapchat did issue a patch for a bug that put permanent versions of unwatched videos into the media gallery on Android phones.
Snaptchat founder Evan Spiegel told Notopoulos that those who enjoyed the service the most would not go to such lengths to view videos.
"There will always be ways to reverse engineer technology products - but that spoils the fun!" he wrote.
Facebook has not yet commented on Buzzfeed's findings, the report said.
