..:: Virus Trojan etc ::..

THE CONCEALER
The concealer  is the  most common  defense  virus  writers  use  to  avoid
detection of  virii.   The most common encryption/decryption routine by far
is the XOR, since it may be used for both encryption and decryption.
encrypt_val   dw   ?   ; Should be somewhere in decrypted area
decrypt:
encrypt:
mov dx, word ptr [bp+encrypt_val]
mov cx, (part_to_encrypt_end – part_to_encrypt_start + 1) / 2
lea [...]