By Dan Gilgoff, CNN.com Religion Editor

The recent disclosure that Mormons baptized the dead parents of Jewish Nazi hunter Simon Wiesenthal by proxy has sparked outrage in the Jewish world. The Church of Jesus Christ of Latter-day Saints has apologized for the baptism, which it says resulted from the actions of a church member acting in violation of church policy. The LDS church vowed to stop baptizing Jewish Holocaust victims in 1995.

But proxy baptism for the dead is a proud Mormon tradition. Here are the basics about how it works and why Mormons do it.

Why do Mormons practice proxy baptism for the dead?

For Mormons, baptizing the dead solves a big theological problem: How do billions of people who never had the opportunity to accept Jesus Christ – including those who lived before Jesus walked the earth – receive salvation? By baptizing the dead, a practice known as posthumous proxy baptism, Mormons believe they are giving every person who ever lived the chance at everlasting life. That includes Muslims, Hindus, atheists, pagans, whoever.

“Mormons believe that there is a place the dead go where they are in ‘spirit prison’ and where they have the chance to accept the Christian baptism,” says Richard Bushman, a Mormon scholar at Columbia University. “But it’s a duty to actually perform Christian ordinance of baptism, so Mormons seek out every last person who ever lived and baptize them.”

Many Mormons are proud of the fact that they attempt to make their faith universal through baptizing the dead. “Historically, Christians have been exclusive,” says Terryl Givens, an expert on Mormonism at the University of Richmond. “Catholics have taught that only Catholics are saved, and evangelicals say only if you confess according to their tradition. Mormons say, ‘No, salvation is open to all people.’”

“In that sense Mormonism is the most nonexclusive religion in the Christian world,” Givens says.

So are all those who are baptized after death considered Mormon?

No. Mormons believe that baptism provides the deceased with the opportunity to join the Church of Jesus Christ of Latter-day Saints, but not the obligation. They don't know if the dead actually accept Jesus. “This is about putting names on the guest list,” says Givens. “They might not go the party, but they are given the chance.’

How does the church decide who is baptized?

The Church of Jesus Christ of Latter-day Saints encourages its members to baptize the dead in their families going back at least four generations.

The church also has teams at headquarters in Salt Lake City and that travel around the world to identify as many people as possible to baptize, whether or not they’re in the lineage of present-day Mormons. “The church is constantly going through parish records, wills, deeds and every other genealogical source so they can extract names and put these people through the temple process,” says Bushman.

The LDS says it does not know how many deceased have been baptized. Experts say the number is in the millions.

There is no way for a person to prevent himself or herself from being baptized by the LDS church after death.

After Jews complained about baptisms of Jewish Holocaust victims, saying such baptisms deny the Jewish identity of those who died because of their faith, the LDS church worked with Jewish groups to stop the practice. But the system of preventing the baptism of Holocaust victims, initiated in 1995, has not been foolproof, as was shown this week with the disclosure about Wiesenthal’s parents.

What are Mormon baptism ceremonies like?

Baptisms for the dead happen inside Mormon temples. Members of the LDS church volunteer to undergo full immersion baptism while the names of the dead are read. An LDS member might participate in 10 or so posthumous proxy baptisms at a time. Young Mormons especially are encouraged to participate, as a way to participate in temple life.

How old is the practice of baptizing the dead?

Joseph Smith, the founder of Mormonism, introduced baptism for the dead in the 1840s. Mormons cite Paul’s letter to the Corinthians as precedent to the practice. “Else what shall they do which are baptized for the dead, if the dead not rise at all?” reads Corinthians 15:29. “Why are they then baptized for the dead?”

For Mormons, baptizing the dead is not seen as a new Mormon tradition but as a practice that ancient Christians practiced and that the LDS Church has reintroduced.

What other questions do you have about the practice? Let us know in the comments below.