afoster, MD5 or SHA of any kind is one way encryption. This is the purpose of even using a hash code. If someone has it, they are unable to decrypt, so to say. Although you could compare a hash with another hash, in an effort to retrieve the supporting text.
And doing encryption in PHP is very simple.
MD5:
[syntaxhighlighter brush=php,first-line=1,highlight=0,collapse=false,html-script=false]hash('md5', 'string text to encrpyt'
;[/syntaxhighlighter]
SHA256:
[syntaxhighlighter brush=php,first-line=1,highlight=0,collapse=false,html-script=false]hash('sha256', 'string text to encrpyt'
;[/syntaxhighlighter]
There are many other ways to encrypt, but for the sake of keeping syntax copacetic, hash function would work great. Craig is right, restoring a recent backup is your best be I believe.