Yes, Skype is secure in many ways because the programmers at Skype have utilized industry-recognized methodologies to secure the data of its users.
Skype uses encryption, digital identity, and independent review of its security systems to stay on top of its security features.
Encryption is utilized to encrypt the data from the computer on your system, may it be a message or voice, as soon as it is entered via the messenger application.
Each messenger carries encryption technology and modules that will aid in encrypting the data.
This prevents data from being intercepted or eavesdropped on while it is being transmitted from your device to your partner’s device.
The encryption algorithms are not custom-built but are industry-accepted and recognized encryption algorithms that have been tested thoroughly.
Another level of security is through the use of digital certificates.
As soon as a user is created through Skype, the Skype servers provide the users with a new certificate.
Based on this digital certificate, Skype identifies and authenticates the users when the user wants to send a message or place a call through to their contacts.
Dual-layer authentication is used when a user wants to authenticate through Skype. First is the user name and password, and the second is the digital certificate, as explained above.
Finally, Skype regularly gets its security architecture and infrastructure evaluated by experts in information security to find out security holes that malicious users might present and exploit. This means Skype adopts a proactive approach towards security rather than a reactive approach.
So yes, in short, Skype is secure, and the messages and calls placed through Skype cannot be sniffed or eavesdropped on while they are on their way across the web.