Siri, the voice-controlled, intelligent, personal assistant that has become the most popular feature of iPhone 4S, is useful and will try to answer all your questions. But don't push it too far or else, it might hurl curses at you, as a 10-year-old British kid found out, to the dismay of his parents.

Siri got into trouble earlier this week when it blurted out dirty words to a young boy in a branch of Tesco in the UK, when he was trying out the hot smartphone.

When 10-year-old Charlie Le Quesne went to a local branch of Tesco with his parents for a late Christmas gift, he asked the Siri on the demonstration iPhone 4S, how many people there were in the world. The personal assistant's choice of reply was unexpected to say the least - Shut the f*** up, you ugly t***, Charlie Le's mother Kim told Coventry Telegraph.

Kim was upset with Siri. It's verbal abuse, Kim told the newspaper. Charlie was with his dad looking at the phones. We can't believe the filth it came out with.

He showed my husband what the phone had said to him and my husband found the store manager and said 'it shouldn't be saying that', she added.

The staff at Tesco had an explanation. They said the iPhone might have been hacked by pranksters, who must have entered some inelegant phrases. Hence the smartphone played it whenever it answers a question

However, what was surprising is that the phone wasn't taken off the display shelf. When the boy went back to the store the next day, the same iPhone was still on the shelf. I'm fuming because they left it there 24 hours later, Kim told Coventry Telegraph.

Tesco told the newspaper they have launched an investigation and have sent the iPhone back to Apple for diagnosis.

We have arranged for the handset in question to be sent for diagnostic testing and we will investigate this issue as a matter of priority with Apple, a statement from Tesco read.