Heidi Klum says it's easy to end up naked in photo shoots.

The German beauty - who posed nude as recently as last year for Allure magazine - has warned some fashion photographers can often take advantage of young models, getting them to take nude pictures, and models need to be vigilant and assertive.

She explained to Ocean Drive magazine: ''When you have a good body, photographers will often be like, 'Yeah let's take this off, and why don't we lose this too'. You can quickly end up not wearing much clothing. You have to be careful and strong at saying no, especially when you're younger and on your own. Not everyone is cool and has your best interest [at heart].''

The 39-year-old catwalk veteran and 'Project Runway' host adds that knowledge of the modelling business comes with experience and she has ''learned not to be scared''.

She said: ''When you're young and pretty, you can't be vulnerable.''

''Not that I'd hurt anyone to get to the top, but you have to bring your hustle and watch your back.''

Heidi also revealed how her legs were insured for an ad campaign with Braun, but bizarrely, one was insured for less than the other.

She said: ''On one knee, I have a scar from when I fell and had to get stitches, so they made that leg less expensive than the other. But I went with it. And obviously, it's all very flattering.''