Some info for anyone not using Avast but thinking about it.
Resident Protection
Resident protection is a special type of task that monitors (according to its settings) all applications being executed and all documents being opened, effectively avoiding virus infection in real time. The task contains a number of so-called providers that are special modules protecting various parts of your computer, e.g. file system or e-mail. Each of these modules can be set up independently.
The resident protection has a special task property - called "default". This task marked as default is started automatically on each start of the operating system and it is not recommended to stop it. It is announced by the "a"-letter icon in the system tray.
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Standard Shield - Provider Settings
Standard Shield checks the programs you start and the files you access. It will not allow an infected program to be started - so, the virus code cannot be activated.
Normal. Default setting.
High. In addition to the default setting, created and modified files will be scanned as well.
Outlook/Exchange - Provider Settings
This setting affects MS Outlook and MS Exchange mail clients only. For setting up the other mail clients, such as Outlook Express, Eudora etc., see Internet Mail Provider.
Normal. Default setting.
High. In addition to the default setting, even read messages are scanned on open and the heuristic sensitivity is set to High.
Internet Mail - Provider Settings
Internet Mail provider is used to protect the e-mail processed by other mail clients than MS Outlook or MS Exchange.
Normal. Default setting.
High. The heuristic sensitivity is set to High.
Script Blocking - Provider Settings
Script Blocking provider is a module protecting your computer against script viruses from web pages. Some web pages might contain a script virus. Normally, running such a virus should not have any consequences, because the scripts are run in a protected mode that prevents them from accessing any files. However, there is a theoretical possibility that you might get infected this way (somebody may find a browser bug that will be exploited by the virus). It is the reason for avast! checking the web pages scripts.
Normal. The setting does not have any meaning for this provider.
High. The setting does not have any meaning for this provider.
"Instant Messaging" - Provider Settings
The Instant Messaging provider protects your communication programs. Many communication programs are capable of sending and receiving files from other users. This way, it is rather easy to get an infected file and spread it further. Some viruses are even able to spread using the communication programs, without the user knowing about it. The Instant Messaging provider avoids this kind of infection. It monitors the folder where the received and sent files are stored. Whenever the content of the folder changes (a new file appears, a file is modified, etc.), avast! immediately performs a scan. On Windows NT/2000/XP/2003/Vista/2008 operating systems, all the files modified by the communication programs are scanned (even outside of the mentioned folder).
P2P Shield - Provider Settings
P2P Shield protects a number of file-sharing programs (so-called P2P programs, Peer-To-Peer). The risk of getting an infected file from a P2P network is rather high due to the uncontrolled flow of data over the P2P networks. Some viruses are even capable of abusing P2P programs to spread themselves, without the user knowing about it. The P2P Shield resident provider will make file-sharing safe.
Network Shield - Provider Settings
Network Shield provider protects your computer from Internet worm attacks. It works similarly to a firewall, even though it does not fully substitutes it. The Network Shield does not require any user interraction.
Note: This resident provider is available on Windows NT, 2000, XP, 2003, Vista, and 2008 only.
Normal. The setting does not have any meaning for this provider.
High. The setting does not have any meaning for this provider.
Hope this helps.