After installing KIS 2013 I have seen that the Video Call and Voice Call buttons are disabled in Yahoo Messenger, while the chat was still working.
This is the fix: In KIS go to:
1 settings
2 advanced settings,network, monitored ports
3 monitor all ports for specified applications
There you search for yahoo messenger and uncheck the check box.
Related article: How difficult is to write a solid software protection (licensing) scheme?
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