Australian BMX cyclist Caroline Buchanan tweeted a photograph from the athletes' village of a container of condoms with a placard reading "Kangaroos condoms, for the gland downunder" with the picture of a boxing kangaroo.
She joked that the container seemed to back up rumours that the athletes' village becomes a hot bed of activity as thousands of competitors complete their events and celebrate after years of working to get to the Olympics.
"Haha, the rumours are true. Olympic village," tweeted Buchanan, whose BMX contest starts on Wednesday.
Barcelona started the trend of supplying free condoms to athletes when the Spanish city held the Olympics in 1992, with the International Olympic Committee (IOC) endorsing the move to help AIDS awareness and prevention. The handouts came with health information.
The London Olympic organisers, LOCOG, have provided 150,000 free condoms in dispensers for the 10,800 athletes at the Games. They are supplied by Durex, part of British consumer goods group Reckitt Benckiser, which paid for the supply rights.
A LOCOG spokeswoman said they were trying to find out who distributed the so-called Kangaroo condoms, with the container shown to hold condoms from Durex rivals Ansell Ltd, an Australian company and Pasante, a private British company.
She said athletes and officials were allowed to bring products into the village for their personal use.
"We will look into this and ask that they are not handed out to other athletes because Durex are our supplier," said the spokeswoman.
Organisers tightly control which brands can be promoted at the Games, striking sponsorship deals with a limited number of companies and trying to stop non-sponsors from getting free publicity on the back of the Olympics.
A spokeswoman for Ansell said her company knew nothing about the issue and it could well be a prank.
"We have had no official participation or association with the Olympics at all," she said.
Lawrence Boon, managing director of Pasante, said his company had no involvement with the distribution of condoms in the athletes' village and he suspected it was a prank by the Australian team.
"We have no association with the Olympics but we did launch a gold condom this year for champions," said Boon.
"With such high teenage pregnancy and STD rates, we try to make people carry condoms by making them fun and interesting."
A Durex spokeswoman said Durex was "proud to be supplying free condoms for the Olympics Games" but declined to elaborate further.
The number of condoms supplied at London tops the 100,000 made available to athletes in Beijing four years ago.
In Sydney in 2000, organisers took delight in having to order 20,000 more condoms after the initial allocation of 70,000 ran out.