I found this info to post on another thread, and thoght I'd share it here:
Not every registered sex offender will appear on this Internet web site. As explained on the Summary of the Law page, approximately 25% of registered sex offenders are excluded from public disclosure by law. Whether public disclosure is permitted is based on the type of sex crime for which the person is required to register.
The Sex Offender Tracking Program is responsible for determining if any sex offender registrant who applies for exclusion from the Internet web site qualifies for exclusion. Registrants whose only registrable sex offenses are for the following offenses may apply for exclusion: (1) sexual battery by restraint (Penal Code § 243.4, subd. (a)); (2) misdemeanor child molestation (Penal Code § 647.6, or former section 647a); or (3) lewd and lascivious acts with a child under 14 (Penal Code section 288) or continuous sexual abuse of a child (Penal Code § 288.5), but only if the person convicted of section 288 or 288.5 successfully completed probation that was granted pursuant to Penal Code section 1203.066, subdivision (c). Click here for a copy of the exclusion form, which must be submitted to DOJ and approved before exclusion will be granted. Registered sex offenders who are granted exclusion from the Internet web site must still register as sex offenders.
http://meganslaw.ca.gov/sexreg.htm
This is in California - I wonder how common this is in other states ?