Security and File Transfers

Skype's file-transfer capability provides a convenient new channel for sharing photographs, documents, and other electronic files among Skype users. Along with this newfound ability, however, comes the risk of inadvertently downloading a file that contains a virus, Trojan horse, spyware, or adware. (For a definition of these terms, see the "Adware and Spy-ware" section later in this appendix).

You must take special precautions when accepting filesin the same way that you would be careful with opening e-mail attachments, sharing files, or downloading directly from the Internet. Before you use Skype's file-transfer capability, make sure that you have up-to-date antivirus software that is configured to scan all incoming files, even from people you know.

IT managers may have an additional concern. Because Skype network traffic is encrypted, it is important to remember that incoming file transfers are decrypted by the Skype application before they can be scanned. This isn't a problem, however, because the "shield" capabilities provided by all the major antivirus software vendors enable real-time scanning.

As a result, if an antivirus product is running, if the virus definitions are up to date, and if a Skype user receives a virus-laden file via Skype, the shield will stop the file from arriving. Today, however, antivirus products simply close the Skype application and display a warning message, because Skype currently does not support centralized scanning for viruses.

On the Microsoft Windows platform, file transfers can be blocked by setting Registry keys for the computers on which the Skype application is running. See Appendix C for more information on blocking file transfers.