MOBILE phone sex games were, until Thursday, available for download from Singtel and M1 websites.
The 'naughty' games on both telcos' websites were removed after complaints from the public to citizen journalism website Stomp.
In a report in The Straits Times, Mrs Sandra Tan, 46, who has two children aged 15 and 18, came across the sex games on the Singtel site two days ago when downloading games for her Samsung Galaxy tablet.
When she called Singtel to inform them, the preschool teacher was told by one of the staff: "I will get my marketing department to look into it."
Her sister, Karen Lim, 47, was alerted. Ms Lim then sent screenshots of the Singtel webpages to Stomp on Thursday.
"We do not know how many children have downloaded such games as you do not even need to log in to access this," told Ms Lim to The Straits Times.
On Singtel's online store, the 'naughty' category appeared next to the Kids and Disney sections. The page featured icons of scantily dressed women and suggestive game titles like "Hot Amateur Housewives" and "Casanova: Sexy Housewives".
M1's version had icons of animated characters in bikini and titles such as "Pictosexy" and "Party Island Sexy Trivia".
Many netizens responded to the post in Stomp and speculated that the Singtel site could have been hacked.
The Straits Times also reported that under the Internet Code of Practice in Singapore, prohibited content includes depiction of nudity or genitalia, sexual violence, homosexuality, incest and paedophilia.
All three telcos here have also signed and spelled out the code of practice in the Voluntary Code for Self-regulation of Mobile Content.
M1's spokesman Ivan Lim told The Straits Times that the incident was 'isolated' and it had removed the sex games and taken action against the content providers.
It is also investigating how the games managed to slip through its filters, however both Singtel and M1 declined to disclose how long the games had been sold online.
"Recently, some mobile gaming content was not presented in the best possible way and this caused concern for a customer. We have taken that feedback seriously and removed the content. We can assure our customers that this was not explicit adult content," said a spokesman from Singtel.
The head of Media Development Authority's video games content and standards, Mr Ernest Khoo, said it had started investigations after receiving a complaint.