getting data without a browser

I have noticed that there are several services that grab data from a web site and then use that data to offer a service of some kind.

Here is an example, overture.com is a click thru advertiser. About a month ago I received several e-mail solicitations from companies offering special reports and services using overtures data. I later found out that Overture did not authorize the use of the data. So my question is, how did these companies grab the data without Overture's help/permission? I don't think any laws were broken because by virtue of having the data on the web it is available for all to access. This company wasn't using a web browser to access the data but must have been using some type of script that pulled the data and put this data into their web pages.

I have also noticed this with many price comparison web sites. They pull the data from several sites without their help and provide a price comparison service.

This all leads me to my security question. How do you prevent others from accesssing the data if you don't want your data used in one of these price comparison engines?

Thanks in advance any info.

 

 

 

 

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