A screenshot of the Google search results for "apple 1" -apple.

A screenshot of the Google search results for "apple 1" -apple.

Google is trying to figure out the cause of a mysterious search bug that returns pages and pages of almost exclusively pornographic and adult results when users enter certain equations or search strings.

A Google search for "-4^(1/4)" at the time of writing revealed the result on a calculator, below which were several pages of porn links with titles such as "four guys and a hooker" and others too lewd to repeat here.

Other search strings that return mostly adult links include:

  • "1 2" -1
  • "1 2" -2
  • "h 3" -h
  • "1 4" -4
  • "apple 1" -apple

The first person to notice the bug appears to be a poster on Quora who wondered what was causing this "equation porn" when users search for contradictory queries.

The Quora post was published in January but Google appears to still be working out how to fix the issue, as the porn results were still present when Fairfax Media tested it on Tuesday morning.

Google search engineer Jeremy Hoffman responded on Friday that Google was working on a "bug fix".

"As a web search query, [-4^(1/4)] is interpreted like [-4 "1 4"], as in 'Find me pages which contain a 1 next to a 4, but which do not contain a 4.'," he said.

"This should return zero results, because it is impossible to satisfy both requirements. However, we have uncovered a bug that causes some web pages to 'match' these contradictory queries," he said. "Since these are the only results that 'match' the query, they are the results that get shown."

Google Australia confirmed the bug but refused to comment further. Some have speculated the reason those contradictory queries return only adult links is because it was a black hat search engine optimisation technique used by porn site operators.