I have a blue cochin who is broody, she has even pulled the feathers off her belly so her skin will be closer to the eggs! I take her out of the nesting box as often as possible.
Your hens may go "broody" at any time in their life. This is when they stubbornly insist on sitting on eggs in order to hatch them into baby chicks. It doesn't matter if the eggs are fertilized or not; some hens will even go broody on golf balls or wooden eggs!
If you have a rooster and want baby chicks, great! But if you don't have a rooster, there are several reasons why you won't want broodiness. First, a broody hen gets grumpy when you try to collect the eggs from underneath her. She might even peck you, so beware! Second, because the eggs are not fertilized, the heat of your hen sitting on them will cause them to decompose at a faster rate - and you want to eat them, don't you? Third, a broody hen plucks out her own breast feathers to line the nest. Ouch! And all for nothing! Finally, a broody hen will just sit and sit on her nest, not eating or drinking as much as she normally would. This will weaken her and deprive her of much-needed nutrients.
To prevent this habit from forming, collect eggs every day. Hens are more likely to go broody on a nest full of eggs.
If a hen has ALREADY gone broody, there are several tactics you can use to break her of this habit. Start by repeatedly removing her from the nest. When Sammy, our Salmon Faverolle, went broody, we'd remove her and carry her around for 10 minutes or so, twice a day. We had to do this for two days before she stopped. For birds that are more determined to be mommies, ice cubes or an ice pack in the nest will usually do the trick. In rare cases, more extreme measures are necessary! Our Australorp, Sweetie, determinedly sat on and melted every ice cube we put under her for a whole week. In the end, we had to put her in "solitary" to break her! (With access to food and water, of course...) When she finally laid an egg again, we knew she was good to go back in the coop.