Updated Canadian student hacker Evan Andersen says Nvidia graphics cards retain content users would rather not be preserved, such as the material appearing in web pages viewed in the supposedly-private "incognito mode" offered by Google's Chrome browser.

The flaws were reported to Nvidia and Google in 2014; the former did not respond while the Chocolate Factory marked the bug as won't fix.

Andersen found the flaw when an "adult entertainment" video he watched re-appeared on his screen on his Apple Mac as he loaded the game Diablo III.

The hacker hypothesises the second coming of his preferred smut came about thanks to a bug in Nvidia drivers that means its GPUs' memory isn't cleared, and therefore ends up reusing bits of images from app to app.

"When the Chrome incognito window was closed, its framebuffer was added to the pool of free GPU memory, but it was not erased," Andersen says.

"When Diablo requested a framebuffer of its own, Nvidia offered up the one previously used by Chrome.

"Since it wasn’t erased, it still contained the previous contents. Since Diablo doesn’t clear the buffer itself - as it should - the old incognito window was put on the screen again."

Andersen wrote an app to scan GPU memory for non-zero pixels and managed to perfectly reproduce a Reddit page.

He considers the bug a "serious problem" for users of shared computers that could be fixed easily; a driver patch could ensure buffers are cleared while Google Chrome could do similar. ®

Updated to add

Nvidia has blamed Apple's OS X for not clearing out the memory used by its GPUs prior to reuse, and says the issue doesn't happen on Windows.