pgp is a public key encryption scheme its a method of effectivly "scamblimg" your data so its difficult for the person without the keys to read it,

keys are made up of very big prime numbers

to crack pgp requires massive computer power and time,

a good link to how pgp works is below

http://www.pgpi.org/doc/pgpintro/

it doesnt really protect you from viruses and worms, i suppose if a program is checksumed (different to pgp) you will know when the file has been altered. Altering a file could mean inserting a virus into it aqnd thus the checksum would not work out, take for example the ISBN number of books the final digit of this is a checksum, work out by adding all the numbers up and then doing the sum of these numbers modulus 7

checksums are used in communications such are p2p and IM to check that the information sent is complete/ un corrupt or not been inserted by a person with ill intent

linux doesn't get affected by malicious exe files
Thats a bit of a throw away comment of course linux can get knakered up, as long as these exe are intended for the linux OS, I think i read that comment somewhere when I was learning networking and Linux, and did some thinking and realised that when you program linux its different to programming windows. There are different calls for libarys and other such things.

Also because the majority of computers in this world that are under attack are windows based this is the reason that allot of tools and virii are created to affect these,

hope that helps, shoot any questions off me, PM me if you need help

i2c