A retired teacher from Merseyside found with more than 150,000 pornographic images of children on his computer has been jailed indefinitely.
William McGrath, 60, of Part Street, Southport, was sent to prison after he admitted a series of downloading and possessing indecent photos.
The judge called McGrath's collection "disgraceful and distressing".
At Liverpool Crown Court the paedophile was order to serve at least two years before parole can be considered.
The court heard McGrath was involved in the widescale distribution of indecent material and encouraged others to become interested, including under-age boys.
Deborah Gould, prosecuting, explained that police found more than 150,000 still images and almost 2,800 video files showing sexual abuse of children, including children as young as 18 months, on six computer drives.
About 700 photographs and hard copy images and reels of cinematic film were also discovered along with emails he sent and received from others with similar interests.
He was arrested in August 2004 when police raided his then-home in Myers Road East, Crosby, but while on bail for 18 months he re-stocked his computer and camera equipment and continued to download hundreds of such images on an almost daily basis.
The judge said: "It appears you have a long standing addiction to this sort of material."
"Any right-thinking member of society would be repulsed and repelled by them."
The offences took place between September 2003 and February last year.
The court was told McGrath developed a particular interest in young boys.
Graham Jeffries, from Merseyside Police, said outside court: "In terms of numbers of images this is one of the worst cases we have come across and I'm glad he's been taken off the street."
McGrath must also sign the sex offenders' register for life and was made the subject of Sexual Offences Prevention Order banning him possessing or using computers, digital cameras, camcorders and the internet.
He cannot be in any residential premises with under-18-year-olds.