Fonterra has apologised for an online Anchor promotion which claimed to estimate whether users were getting enough calcium, but actually told everyone they needed more.
The milk producer said the faulty test, which sparked a complaint to the Advertising Standards Authority, was due to a computer bug.
The Calci+ BoneHealth Calculator promised to "help you find out how well you're looking after your bones and what more you can do to protect yourself from risk of osteoporosis and fractures in later life".
But complainant Kathleen Lafferty said she filled out the calculator multiple times with varying details, and found it always gave a "low" result.
"This test is bad science and provides misinformation on the side of fear mongering. It targets vulnerable people."
In response Fonterra Brands New Zealand (FBNZ) said the calculator, launched in 2012, was developed in collaboration with Osteoporosis New Zealand, and was intended to give either 'low', 'medium' or 'high' results.
It was alerted to the fault through a Facebook comment by a user. FBNZ regretted the calculator wasn't working correctly, but said the problem was fixed as quickly as possible.
"This was an isolated issue due to an unknown bug in the website which has now been rectified. The calculator now operates in the correct manner."
