During the Vietnam war, copper became harder to find in the US leaving wire manufactures to find a conductive metal that was readily available and Aluminum wiring became main stream.
While aluminum (or AL wiring) was cheaper, the devices to connect to the AL wiring were not, sometimes costing as much as 10 times or more per device. This is where the problem with AL wiring really starts. As home improvement stores and do it yourself became more popular, electrical repairs became something the DYI guy did himself and while at the store often would purchase the 50 cent receptacle over the $5 receptacle as a replacement.
If you look on the back of any wiring device it is marked AL or CU. CU devices are ONLY for copper wiring while AL devices are ONLY for aluminum wiring. The problem is most DYI people do not know this and since CU receptacles are generally 50 cents, they purchase CU receptacles. If you think back to your chem classes, CU and AL do NOT mix well and will create a chemical reaction when combined, especially when electricity is introduced. The generally will result in heat, causing the metal to expand and thus a loose connection is born. Loose connections cause arcing and arc's lead to heat, excessive heat often leads to equipment failure which can lead to fire.
So what to do if your house has AL in it? My suggestion has always been to call a licensed electrician and have the house pig tailed with copper wire. This is 1/5 of the cost of re-wiring and can be done in a day without a mess. This will allow for the less expensive CU devices to be used safely and will (as much as you can) eliminate the fire risk. As I told many customers when I was in the field, I would have no problem with my Mom living in a house with AL wire, provided I had ensured it was properly installed and maintained.