Text messages have been mysteriously altered between sender and recipient in at least 20 cases, prompting a Telecom investigation.

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Salvation Army church leader Steve Molen discovered the glitch last week when he sent a text to 10 people to remind them of an upcoming dinner.

It ended on a lighthearted note with "bring a date or your muma but would prefer it if you bought [sic] a youth and plenty of food should be a great night so see you there six o'clock".

TEXT MIX-UP: What Steve Molen's wife received.

However, one recipient – his wife Faye – received a message that read "bring a date or your muma but would prefer it if you bought me she setting a bad example for me".

Mr Molen, of Newtown, contacted Telecom's call centre and was told he wasn't the first to experience the problem. "[The call centre worker] said it was a software fault that adds lines to the last part of people's texts ... and there had even been swear words added on to some messages.

"I said to him does that mean I could send a text to my boss that inadvertently tells him to eff off?"

Mr Molen was concerned that people may be unknowingly receiving corrupted texts on a regular basis. "Telecom has a responsibility to make sure that, if you send a text, it is what ends up being sent."

Telecom sponsorship and mobile PR manager Rebecca Ingram said the problem was "extremely rare" and the cause was being investigated. It was "highly unlikely" that offensive words could randomly appear in a corrupted message.

Mobile users were not being hacked, she said. "Any additional text content is quite randomly appended or is a result of the existing text message being jumbled."

But Telecommunications Users Association chief executive Ernie Newman was sceptical. "It doesn't seem to me that a random insert into a text message would come out with an intelligible message at the end of it ... it seems to me that somebody must be hacking it."