Intelligent IM Filter: URL Filter

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Use the URL Filter tab to control the way in which hyperlinks are handled during an instant messaging (IM) conversation.

Enable URL filtering

To restrict the use of uniform resource locators (URLs) in your Office Communications Server environment based on the options you specify, select the Enable URL filtering check box, and then specify the appropriate options on the URL Filter tab.

Block all hyperlinks, both intranet and Internet, that contain any of the file extensions defined on the File Transfer Filter tab

To block any active intranet or Internet hyperlink that contains a file with an extension listed on the File Transfer Filter tab, select this check box. When an instant message is blocked, an error message is displayed to the sender. When selected, this option takes precedence over all other filtering options.

Important: Ensure that you configure the File Transfer Filter tab with the file extensions that you want to block. Filtering of file extensions is limited to standard file names. Filtering may not work with file extensions imbedded in other names.

Allow local intranet URLs

To block only active Internet URLs, select this check box. If you select this option, URLs for locations within your intranet are passed through the server; however, individual servers running Office Communications Server 2007 R2 may define an intranet URL differently, depending on the browser settings on the server.

Hyperlinks handling

To specify how hyperlink blocking is implemented for instant messages, click the appropriate option:

  • To block all instant messages that contain a hyperlink, click Block instant messages that contain hyperlinks. If you select this option, Office Communications Server blocks delivery of messages containing active hyperlinks, and the sender receives an error message.

  • To convert links in instant messages to plain text and send a modification notification for each instant message that contains a hyperlink, click Allow instant messages that contain hyperlinks, but convert the links to plain text, and then type a notice of no more than 300 characters to display to recipients to notify them that the hyperlink has been modified from its original format. If you select this option, URLs in messages are sent through the server, but these links are prefixed by an underscore so that the links are no longer active and a user cannot click them.

  • To insert a warning at the beginning of each instant message that contains a hyperlink, click Allow instant messages that contain hyperlinks, and then type a warning of no more than 300 characters to display to recipients to warn them about the potential risks in clicking active hyperlinks.

Enter the prefixes, separated by a space that you want the URL filter to block

To specify prefixes to be used to block URLs, type them in the list. A default list of URL types appears in this box. You can add URL types to or remove URL types from this list. All entries except for href must end with a period or a colon or with an asterisk followed by a period. Valid entries in this box can contain any characters in the set of valid URL characters except the asterisk (*). The set of valid URL characters is: #*+/0123456789=@ABCDEFGHIJKLMNOPQRSTUVWXYZ^_` abcdefghijklmnopqrstuvwxyz|~

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The Intelligent IM Filter application helps protect your Office Communications Server deployment against the spread of the most common forms of viruses with minimal degradation to the user experience. Use Intelligent IM Filter to configure filters to block unsolicited or potentially harmful instant messages from unknown endpoints outside your organization's firewall. You configure filters by specifying the criteria to determine what to block, such as instant messages containing hyperlinks and files with specific extensions.

The Intelligent IM Filter increases the amount of CPU resources required to process URLs in a message. This increase in CPU demand also affects the performance of Office Communications Server itself.

URL Filter

When an instant message travels from one server to another, the following general guidelines apply:

  • If a server blocks an IM, the client that sent the message receives an error. Subsequent servers do not receive the blocked IM.

  • If a server (S1) modifies a URL by converting it to plain text and adds a modification notice, any subsequent servers that receive the message do not edit the notice sent by S1. If a subsequent server with the same settings receives this message, the server does not change, remove, or add to the modification notice from S1 is retained. If a subsequent server with different URL filtering settings receives this message, S2 for example, S2 can apply its own IM filter to block, modify, or add a warning to the IM. Any modification notice or warning from S2 directly precedes the modification notice from S1.

  • If a server (S1) adds a warning to an IM that contains an active hyperlink, a subsequent server (S2) that receives this IM can have different IM filtering settings that apply a different action based on this active hyperlink present in the IM. The IM filter on S2 can block the IM or modify the URL by converting it to plain text. If S2 is configured only to add a warning for this URL, the earlier warning added to the IM by S1 would be replaced by the warning configured according to the IM filter on S2.

  • As a special case, if the sending server (S1) filters intranet URLs but allows active links with only a warning, then S1 will insert a warning in any message with an intranet URL; however, if the subsequent server (S2) that receives this message permits intranet URLs, then S2 will remove the warning text from the message.

For details, see the Operations section of the Office Communications Server Technical Library.

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