Protection for children or state aide for vigilantes?

A government minister has gone to the US to investigate the so-called 'Megan's Law' system, which allows the public to know the addresses of convicted sex offenders. Here in the UK there has been a campaign for a similar system, dubbed "Sarah's Law" after Sarah Payne. But I'm not convinced this would be a good move.

(As an aside, there's something about the way the law is named after a murder victim that sits very uneasily with me. I'm also not sure that such a law would have actually prevented the tragedy - neither the victim nor murderer were in their home area.)

What especially worries me is that I can go onto websites such as California Megan's Law website and within a few clicks I can find the home addresses of offenders. When The News of the World "named and shamed" alleged sex offenders several years ago there were vigilante mobs terrorising not just the convicted but also the alleged, the misaccused and innocent bystanders. Can releasing such information to the public really bring benefit?

And what difference would such a law make? Informing parents when a convicted sex offender moves into "the area" can encourage complacency when they are not informed. (And just what does "the area" actually mean? Would it be the neighbourhood, the ward, the town, the borough, the county or what? Or would it be something arbitrary like everyone within one mile of the address?) Most sexual abuse takes place within families - this is difficult to inform without breaking the victims' anonymity. And many sex offenders, especially those with convictions, would seek to minimise the risk by going out of "the area". Or they would go underground - the sex offenders register in the US is estimated to have about 80% compliance, compared to 97% in the UK. Is such a law really going to be to the benefit of protecting children?