It's a tentative to detect which software is used to build the site; in the specific, they are trying to understand if the site is built with Visual DataFlex, a forth generation programming language geared towards creating database and client/server type applications. The .dfr extension is used for the Visual DataFlex license file.
It's similar to those tentative to access a URL used from WordPress to understand if the site is built with WordPress.

Once they know what is used to built the site, they can take advantage of specific vulnerabilities to get access to reserved information or cause denial of service.

It's a tentative to detect which software is used to build the site; in the specific, they are trying to understand if the site is built with Visual DataFlex, a forth generation programming language geared towards creating database and client/server type applications. The .dfr extension is used for the Visual DataFlex license file.
It's similar to those attempts to access a URL used from WordPress to understand if the site is built with WordPress.

Once they know what is used to built the site, they can take advantage of specific vulnerabilities to get access to reserved information or cause denial of service.

It's a tentative to detect which software is used to build the site; in the specific, they are trying to understand if the site is built with Visual DataFlex, a forth generation programming language geared towards creating database and client/server type applications. The .dfr file is the file containing the licence for Visual DataFlex.

It's similar to those tentative to access a URL used from WordPress to understand if the site is built with WordPress. Once they know what is used to built the site, they can take advantage of specific vulnerabilities to get access to reserved information or cause denial of service.

It's a tentative to detect which software is used to build the site; in the specific, they are trying to understand if the site is built with Visual DataFlex, a forth generation programming language geared towards creating database and client/server type applications. The .dfr extension is used for the Visual DataFlex license file.
It's similar to those tentative to access a URL used from WordPress to understand if the site is built with WordPress. 

Once they know what is used to built the site, they can take advantage of specific vulnerabilities to get access to reserved information or cause denial of service.