My cousin found this spider at his place. He lives near Milan, Italy, in a small town. It's a humid region, around there the are a lot of fields but it is a 15 km from the city. It's still hot in these days. He told me that in the picture it seems a little bit too yellow. In reality it is more of an orange shade. He has never seen anything like that around there. Any clues?
Judging by the photo and the web it may be an orb-weaver spider of the family Araneidae. Orb-weaver spiders get their name from the circular webs they spin. It's possibly an Araniella cucurbitina, also known as a Cucumber spider, which are commonly observed hanging head down in it's web. Several photos can be found at eurospiders.com.