A computer algorithm has replaced humans to assess the security risk of asylum seekers, criminals and visa overstayers in Australian immigration detention centres.

The new Security Risk Assessment Tool, designed to assess "individuals who are considered to pose an unacceptable risk to the community", was quietly rolled out in September.

The assessment system is in place at Melbourne's high-security Maribyrnong immigration detention centre. Credit:Shannon Morris

A spokeswoman for the Department of Immigration and Border Protection said the SRAT was guided by the detainee's behaviour both during and prior to detention, any signs of violent or aggressive behaviour and their known associations.

"It also considers a each detainee's individual circumstances including age and health," she said.