Skype is an immensely popular voice and collaboration service. This makes it an attractive target for spammers and scammers. By investing a few minutes to adjust your Skype privacy you can avoid spam and privacy leaks. Here's what I recommend as best Skype practices.
Only allow calls, video, screen sharing and IMs from approved contacts. You can control who is allowed to place voice and video calls to your account, send you instant messages, and who can share your screen through Skype's Privacy Advanced Options. Begin by launching Skype. From the Skype menu pulldown, choose Privacy... Choose Privacy Settings and click on Show Advanced Options.
Windows users should consider these settings:
Allow Calls from... people in my Contact list only
Automatically receive video and screen sharing from... people in my Contact list only
Allow IMs from... people in my Contact list only
Under Skype WWW options, uncheck
Allow my online status to be shown on the web
Accept Skype browser cookies
Manage your Contacts intelligently and you should be reasonably insulated from spam. (You can't be entirely free of spam since one of your Contacts might have his Skype account compromised and the attacker could use the compromised account to spam anyone the attacker can reach from that account.)