OS 10.6.6: security updates and upgrades

Question

i bought an iMac about a year ago, with OS being 10.6.6. I haven't brought it yet on the web ( i use this portable PC ).
Before getting it on the web, i'll obviously will have to
   1 - update to 10.6.8   : is this presently the "top" update for 10.6 ?
    2  -  from what i read snow leopard is a leap, SECURITY- -wise, behind even 10.7 ( mountain lion ). QUESTION: is an UPDATED snow leopard as web-secure
           as a 10.7,     8   or even    .9    ?

Answer 1

There are many forms of ‘Malware’ that can affect a computer system, of which ‘a virus’ is but one type, ‘trojans’ another. Using the strict definition of a computer virus, no viruses that can attack OS X have so far been detected 'in the wild', i.e. in anything other than laboratory conditions. The same is not true of other forms of malware, such as Trojans. Whilst it is a fairly safe bet that your Mac will NOT be infected by a virus, it may have other security-related problem, but more likely a technical problem unrelated to any malware threat.
You may find this User Tip on Viruses, Trojan Detection and Removal, as well as general Internet Security and Privacy, useful: The User Tip seeks to offer guidance on the main security threats and how to avoid them.
https://discussions.apple.com/docs/DOC-2435
More useful information can also be found here:
www.thesafemac.com/mmg
It would be at least partly true to say that the later the version of OS X, the better the security. The downside is: will you existing applications run? 
(NB: PowerPC applications can still be run in Snow Leopard using Rosetta, but they will not work in later versions of OS X.)
Check via Software Update whether any further updates are required, particularly to iTunes.
You should now see the App Store icon in iTunes, and you now need to set up your account:
http://support.apple.com/kb/HT4479
You can now upgrade to Mavericks OS 10.9 for free IF you have one of the following Macs, with not less than 2GB of RAM, and at least 8GB of available space on your hard drive:
iMac (Mid-2007 or later)
MacBook (13-inch Aluminum, Late 2008), (13-inch, Early 2009 or later)
MacBook Pro (13-inch, Mid-2009 or later), (15-inch, Mid/Late 2007 or later), (17-inch, Late 2007 or later)
MacBook Air (Late 2008 or later)
Mac Mini (Early 2009 or later)
Mac Pro (Early 2008 or later)
Xserve (Early 2009)
iCloud system requirements:
http://support.apple.com/kb/ht4759
If you cannot run Mavericks you can purchase the code to use to download Lion from the App Store (Lion requires an Intel-based Mac with a Core 2 Duo, i3, i5, i7 or Xeon processor and 2GB of RAM, running the latest version of Snow Leopard):
http://store.apple.com/us/product/D6106Z/A/os-x-lion
or Mountain Lion:
http://store.apple.com/us/product/D6377Z/A/os-x-mountain-lion