Traditionally, a security clearance is a background check process performed by states on prospective employees for sensitive documents. It usually involves enlisting the help of intelligence agencies and trying to find out if the prospective employee might have had a sad past that made them unsuitable for the position in question.
People who wish to be appointed as ambassador attaches, secretaries of state, etc. usually go through this type of security check. The idea is to avoid putting people from dubious backgrounds, or worse, spies, into the sensitive position in question. You can also get more information about employment vetting checks via https://www.first4freelancers.co.uk/screening-vetting.
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But also for organizations, there is an increasing argument for security checks. Many organizations have adopted it as a core employment policy, as part of what is known as pre-employment screening, which checks the sensitive security records associated with prospective employees.
Of course, organizations that are not part of a government structure usually cannot gain access to information that governments use in their own security clearance procedures. But using such information would be considered redundant for the needs of a typical organization, as they carry out security checks before hiring.
Most of the time, a detailed examination of the potential employee's criminal history is sufficient to prevent introducing undesirable components into the game. However, it's also crucial to consider other factors that can affect security, such as the prospective employee's present location, credit history, and perhaps even previous employment history.