While browsing through the Macromedia Actionscript Errata, i found the following new property, which is very,very useful:

System.security.allowDomain

Availability:
Flash MX

Usage:

System.security.allowDomain(domain1, domain2,....domainN)

Description:

Allows Flash MX movies in the identified domains to access objects and variables in the Flash MX movie that calls the allowDomain command.

Example:

The domains can be formatted in the following ways: domain.com, domain.com, or IPaddress.

Scenario:

loads . MovieA.swf contains the command System.security.allowDomain("shockwave.com") . Therefore MovieB.swf will be able to access MovieA.swf's objects and variables.