Is it legal to use software to automatically extract data from several websites and then use it on another website?
Taking data from a website that isn’t OFFERING that data is hacking. Screen scraping or web extraction is a process wherein data that is publicly available on the website is extracted and stored in a database format.
Websites that want you to use their data are generally the ones that offer API’s or feeds, either RSS or in the case of commercial entities, their IT people will normally help to provide information to customers (like stock listings or prices) because it helps you to sell more, and thus buy more from them.
Providing feeds to consume the data is new concept. There many websites that that don’t provide feeds, but you can access the data via a login or perfoming a search on the website to locate the desired data. Writing an automated script to do the login and / or perfoming searches to get the data out is not illegal – but care must be taken that you donot you use up their bandwidth and disallow other visitors. They might not be overly impressed and ask you to stop doing it.
Lastly, there are websites that expressly forbid you take their data under their terms and conditions. If you do try to scrape these websites, they will certainly termintae the access to their website.
It is wise to read the terms and agreement policy of a website before you attempt to scrape data from it and respect it. Most sites will have their terms and conditions for accessing the data. Also, necer try to extract data that a company has not published online. That is hacking which is illegal.