CLOSE PROX ACR-MLG GA-SMT DURING VISUAL APCH TO PARALLEL RWYS.

Narrative

APCH WAS VECTORING US FOR AN ILS TO RWY 26R AT ATL. ABOUT 12 MI OUT APCH TOLD US TO PLAN ON SWITCHING OVER TO RWY 26L LATER IN THE APCH WHEN WE HAD THE FIELD VISUALLY SO HE COULD WORK ANOTHER ACFT; SMT INTO RWY 26R. WE THEN HEARD APCH TALKING TO THE OTHER ACFT WHO APPARENTLY HAD US IN SIGHT. APCH ACKNOWLEDGED HE HAD US IN SIGHT--TOLD US WE WERE CLRED FOR RWY 26L AND CLRED THE SMT ACFT FOR RWY 26R. HE ALSO TOLD THE SMT TO KEEP US IN SIGHT. DUE TO THE POOR VIS AT THIS PARTICULAR TIME; OUR ATTN WAS DIRECTED TOWARDS ALIGNMENT FOR RWY 26L. THE VIS IMPROVED SHORTLY THEREAFTER AND I RPTED US ESTABLISHED FOR RWY 26L (CONFIRMED BOTH VISUALLY AND BY NAVAIDS). JUST AS WE HAD CALLED TWR CONFIRMING RWY 26L; THE CAPT CAUGHT SIGHT OF THE SMT ACFT WHO APPARENTLY OVERSHOT THE FINAL COURSE FOR RWY 26R AND WAS DRIFTING TOWARDS US. THE CAPT TOOK PROMPT EVASIVE ACTION (NON VIOLENT) AND I NOTED THE SMT TURNING BACK AWAY FROM US. NO ONE (NOT APCH OR TWR) ADVISED US OF HIS CLOSE PROX! THIS WHOLE PROC NEEDS TO BE CHANGED OR AT LEAST RE-EVALUATED. OUR SAFETY DEPENDED ON THE SMT ACFT DRIVER'S COMPETENCE.