Some big marketing company hire the hackers and create crawler which are mostly used to theft the personal data from the websites. Some buy these data from other company for marketing purpose.
For example think you started a small business but you don’t have any records to publish your products in front of useful clients then you hire some marketing company which provide the specific data to you or do bulk email marketing for you. In a short time period you get lots of lead and sale will go up.
These company use the spamming technique like bulk sms, get information from website with the help of crawler. Some time manully they get the information of clients of specific category. A big source of these information is directory website or portal in which you get the personal details. Like some matrimonaial website , a business directory and a property portal. They sale the data to special person about specific category.