Wiring technology has moved on considerably, and some older cabling types still found in Australian homes carry real, recognised risks.
Common in homes wired before the 1960s-70s, VIR insulation becomes brittle and can crumble with age, exposing bare wire. It's considered a fire and shock risk and is generally recommended for replacement wherever found.
Used in some homes mainly during periods of copper shortage, aluminium wiring expands and contracts more than copper, which can loosen connections over time and increase the risk of overheating at joints and outlets.
You often can't tell without an inspection, especially in ceiling and wall cavities. Older homes that haven't been rewired since original construction are the most likely candidates.
A licensed electrician can inspect visible wiring (at the switchboard and accessible points) and advise whether further investigation or a full or partial rewire is warranted. This is also a standard check as part of a pre-purchase electrical inspection.