If you want to block some countries from accessing your store:
go to http://www.countryipblocks.net
1) in "select format" choose: ".htaccess deny"
2) select countries you want to block holding CTRL and left clicking to select
3) click "Choose countries"
See screen shot: http://screencast.com/t/g4KjNsmR5
Copy all the code in the result and add it at the end of your .htaccess file or email to firstname.lastname@example.org for the installation:
See screen shot: http://screencast.com/t/OPrk0wkvUmu