Two things on the Apple front. Skype has fixed an easily exploitable weakness on the Mac with their new version 188.8.131.525. When you launch an older version it should prompt you to download the the new version. Be sure to do so.
Purveyors of Fake AV or Scareware are actively targeting Safari with programs like Mac Security, Mac Defender, and Mac Protector. These are not legitimate security programs.
If you’d like to add legitimate AV software, Sophos has been getting great reviews for their free Home version. You can find it by searching for “Sophos Anti-Virus for Mac Home Edition”. At this point, real AV software on your Mac is no longer optional.
A configuration change may also be a good idea. Safari defaults to run “safe” files immediately after downloading. Seems the bad guys figured this out and all is not safe in the safe files. To change this setting: Launch Safari | Safari | Preferences | General | Uncheck Open “safe” files after downloading.