That's clever, they've hidden the fact that they are using base64_decode by putting all the letters into a randomized string and pulling them out in the correct order again. Since scanners can easily detect and red flag base64_decode, they've done this to hide it's usage in an attempt to go undetected:
$sF[4] = B
$sF[5] = A
$sF[9] = S
$sF[10] = E
$sF[6] = 6
$sF[3] = 4
$sF[11] = _
$sF[8] = D
$sF[10] = E
$sF[1] = C
$sF[7] = O
$sF[8] = D
$sF[10] = E
I suggest following the instructions that WFSupport and I posted earlier. This is some nasty stuff you don't want hanging around in WordPress.