There is very little difference between the two. Not enough to spend the money.
As far as the other part of your question...Well there is so much info on these Forums about Viruses, Worms, Spam, Corrupt Files and anything and everything else, you are just going to have to take the time and do a LOT of Research and Reading. There is NO Quick answer, but it's all right here, somewhere.
There is a Forum Search Function.
Or do what most people do and go off and get infected and then come back in here asking for help to rid themselves of the Trojan they just downloaded.
