Keep in mind that the 90/180 rule only applies to tourists:
Can I undertake paid work or study while I’m in Spain?
If you enter Spain under the 90/180-day rule, you cannot carry out any paid employment or studies. If you wish to do either of these, you must apply for the appropriate visa before you arrive.
If YosserHughes intends to work for Malta-based company, they will need a C or maybe even D visa for Malta.