Being safe on the internet (was Re: Here we go again - ISP DPI, but is it interception?)

[Roland Perry]

In article <20100804150343.00007a3f at surtees.fenrir.org.uk>, Brian 
Morrison <bdm at fenrir.org.uk> writes
>> >> And I see from the 'Update  History' that this is the 11th version 
>> >>it has installed in a little  under a year!
>> >
>> >You should be pleased that they fix the things they know about....
>>
>> On the contrary, I'm displeased they have so many vulnerabilities in
>> the base product.
>
>*Everybody* has many vulnerabilities in their products, so getting them
>fixed is better than not doing so.

It seems to be worse than that... why are these products so susceptible 
to vulnerabilities? For example, one that used to occur over and over 
again was "buffer overflow". Surely there must be programming (or memory 
management) techniques that could eliminate them entirely?
-- 
Roland Perry