Domain name front running is the act of a domain registrar using insider information to register certain domain names for the sole purpose of re-selling them or to earn profit.
Often front running is conducted via popular whois searches; where some whois websites can track what you look up. (NOTE: the Above whois does not log whois searches)
Employees of Registrars could then use this information to purchase popular domains before you get the chance to. For example if you see a domain name that is available to be registered and you search the domain via a whois search, if an employee registers the domain before you, due to your whois search, it is called Domain Name Front Running or Domain Spying.
There are other ways domain name front running can occur, such as: registrars, registries, software or DNS operators. It could also be possible that a registry is providing root DNS data to their registrar clients for the sole purpose of registering more domains.
One advice is, DO NOT type a domain name into a browser to see if it exists, not only is this unreliable but the sites you visit can be tracked via your ISP. ISP’s can sell data including non-existent domain name results, called DNS error logs.
The term domain name front running was first used by retired stockbroker and domain investor, Daniel Stager, who likened the process to a stockbroker illegally putting their own financial gain before their clients.
The issue in regards to domain name front running is often there is little accurate evidence to prove that someone is spying or how they spy on you. It could be that another user has also thought the same as you, independently.