Is there any point to having these two providers active? Won’t any incoming email virii be caught by the standard shield? I suppose the same could be asked about the P2P shield as well.
Outlook/Exchange plugin works with full MS Outlook (not the Express).
Internet Mail provider works with pop3/smtp mail clients (OE, Thunderbird, etc. etc.).
Email messages are a very common source of virus. These providers work specifically on them, avoiding that virus could be even saved in your disk. Standard Shield needs the file saved in your disk to act.
It is called protection in depth, the best policy is the stop the virus getting on the HDD (inbox, etc.) in the first place as once active/established it is much more difficult to remove/deal with. The mail scanners, web shield and other provides give that first line of defence with Standard Shield as the fall back.
Well, standard shield can catch the virus when it is written on the disk - depending on your settings this might be even later - when it tries to execute itself from the disk location.
When you download viruses via e-mail message or web page, usually you are tricked to execute the virus. You click somewhere where you should not or something like that - these are the easy ones. However it might be also the application displaying the mail or web page that gets tricked. The virus exploits some security hole (or we can call it simply bug) in the application. There were many such infections via unpatched copies of Internet Explorer or Outlook Express. In this situation some code is executed before the virus body is written to the disk and despite the fact it usually gets written shortly after some harm might already be done.