Your description may also refer to the white-backed garden spider which carries white markings on their legs as well as their back. However, the colour may range from cream to yellow on some spiders, and their abdomen is shaped like a leaf. Again, this type of spider is not dangerous, and they can be good for pest control.
Another form of spider you may be referring to is the wolf spider, which is of a fuzzy black appearance accompanied by white or grey markings. They are larger than the average spider, with the body measuring up to about an inch long. You need to keep in mind that these spiders will bite you, so you will need to consult a doctor if you are bitten but don't panic because the venom won't kill you.
The most dangerous spider that sometimes has white spots is the black widow. You may think that the majority of black widow spiders have a red shape on their bodies however; the male and young black widows can have white spots. A bite from one of these spiders is very dangerous so avoid them at all costs.