Maybe you should look at the source code

When eBay acquired Skype in 2006 for $3 billion, they didn't even blink at the source code and were satisfied with a binary that was "protected" (read obfuscated). As revealed now, Skype seems to contain a backdoor that remotely shuts down Skype by disabling encryption. This stunning revelation seems to indicate that it might be a good idea to at least have a look at the source code before you put money on the table for a piece software.

refs:
Twilight in the Valley of the Nerds
TmcNet