Anyone who believes in Christ is a Christian (by definition). They might worship differently, but so do all of the various sects who worship various different Christian bibles.
Some professed Christians worship Satan, in secret. For example, Presidents George Herbert Walker Bush and his son, George W. Bush, both were members of Skull and Bones in Yale. Skull and Bones had its own bible and own religion. Members would do things like steal the skeletal remains of a famous Indian (which is what Prescott Bush did). All members sit around cauldrons with weird Satanic ingredients (eye of newt (Gingrich?), toe of toad, etc). As they stir the cauldron, they summon Satan though chants (and not by chance).
There are many Christians in the world, including Mormons (Church of Latter Day Saints).