They're not notifying Gardaí of address changes, despite being obliged by law.
More than 400 convicted sex offenders have disappeared from Garda surveillance since 2010.
The Irish Daily Mail reports that 421 individuals with sex convictions left their registered addresses without telling Gardaí, despite being legally obliged to do so.
Those convicted of sex offences since 2001 are placed on the Sex Offenders Register.
Following their release from custody, they are required to keep Gardaí notified if their address changes.
These requirements also apply to criminals who have come to Ireland having committed sexual offences overseas.
