Parents were sent into a blind panic when a school mistakenly sent out a text alert saying their children had gone missing.
Hundreds of mums and dad Wadebridge secondary school in Cornwall each received a text reporting their child had not arrived.
Parents said they were left 'frightened to death' by the error.
Some imagined their kids had been involved in an accident, while others thought they were playing truant.
Headteacher Tina Yardley has now apologised for the error, saying they had been 'completely unaware' the automated messages had been sent out until the switchboard became jammed with worried parents.
She said the mistake had been caused by an 'administrative work flow issue'.
The electronic alert, from Truancy Call, went out at around 2pm on Monday February 2. It is usually sent to inform parents that their child has missed morning registration.
One grandmother said that her daughter, who has a child at the secondary school, had been 'frightened to death' by the text.
She said: "She went haring to the school. She thought something had happened to my grandchild. She's still in a state of shock now."
Sharon Meehan, 42, who has a son in Year Seven of the school, said her husband was left 'going mental' with worry after receiving the message.
She said: "It is worrying though, especially when you are at work and your son has only just started at the school.
"What's worse is that it took me half an hour to get through and this is the second time this has happened to me. The school need to sort it out."
Gabriella Cleave, 38, received the text to say her 12-year-old son was absent from the school which 'sparked off a big panic'.
She said: "All kinds of potential scenarios were going through my head. I thought the bus might have crashed or someone might have grabbed him – all kinds of things were going through my mind.
"It was worrying. I was trying to phone the school for about 30 minutes but I could not get through as it was engaged.
"I just thought – where on earth is he? Jake is not one to play truant and I had never seen a message like that before.
"After a while I phoned a friend, who said she had got the same message about her son and we started to think someone might have hacked the school's message system."
Miss Yardley, the school's headteacher, said: "As soon as we were aware that something was wrong we sent another message as soon as we could to inform parents that there was a computer error and to try and alleviate any worry. "We do realise and understand the anxiety and worry that this message caused some parents but as you can see it was not something that we had control of, but we will do everything we possibly can to make sure it doesn't happen again."
The school said the error was not caused by anti-truancy software malfunctioning but by an 'administrative workflow issue'.
A spokesman for Truancy Call said it had been down to 'human error' at the school.
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