According to the Prevention of Fraud Act passed in December 2006, it is considered that an offshore company is domiciled in Spain for Corporation Tax purposes when:
1) The assets of the offshore company, directly or indirectly, are property or rights to be fulfilled or executed in Spain or
2) When the activity of the offshore company take place in Spain unless
3) The offshore company can prove that its address and management are effectively carried out in the offshore territory and also that the setting up and operation of the company are consequence of valid entrepreneurial and business measures, other than mere management of assets or other rights.
This means that in practice most offshore companies with assets in Spain will be considered the same as a Spanish resident company and therefore will have to declare in Spain all assets and income (explicitly or presumed) from all over the World.