SMART Failures in multiple desktop PCs

I have a client with approx 40 x Acer Veriton N282G computers, and each of these contain a WD 3200BPVT Scorpio Blue 320GB 2.5" SATA drive. They are approx 3 years old, just out of warranty and run up to date Windows 7 pro, up to date virus software and the clients general applications which are fairly low intensity.

They have been running fine with very few problems, however, in the space of just 3 weeks, 4 of the units have presented a SMART failure warning in windows, and the hard drives have completely failed within a few hours of that.

Obviously, as they are out of warranty there is not a lot I can do about it, but it is concerning that an unusual error that has never appeared before should present itself on 4 different computers in such a short space of time.

Unfortunately, time between error and complete fail has been too short for me to get hold of one and run any diagnotics on it so far.

The client is obviously concerned that this may happen to all 40 PCs in a very short amount of time.

Can anyone suggest a cause of this, and if there is anything I can do \ check to help prevent further instances. Or if anyone else has had a similar experience?

There are too many different possibilities to consider from a specific update to a general power failure. Each system should be diagnosed individually.