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 message or voice as soon as it is entered via the messenger application.

Each messenger carries encryption technology and modules which will aid in encryption of the data. This prevents the data from being eaves dropped or sniffed while in transit from your system to the system of your contact you are communicating with.

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 messenger, a certificate is provided by the servers at Skype to the users.

Based on this digital certificate, Skype identifies and authenticates the users while the user wants to send a message or place a call through to their contacts.

Dual layer authentication is used while a user wants to authenticate through to Skype. First is the user name and password and the second is the digital certificate as explained above.

Finally Skype regularly get is security architecture and infrastructure evaluated by experts in the field of information security to find out security holes that might be present and exploited by the malicious users. 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 that are placed through Skype cannot be sniffed or eaves dropped while they are on their way across the web.