Judge Brian Capstick, passing sentence, told Timothy Tobin, 25, that it was clear he posed a serious danger to the public and "young people in particular".
The judge added he had to pass a life sentence: "It seems to me probable you will commit grave offences in the future and the consequences of those will be specifically injurious to the victim."
Judge Capstick had studied probation reports on Tobin which described him as "not being concerned" at the health risk he presented in any sexual encounter.
Despite a conviction for indecently assaulting an 11-year-old girl and the charge he was jailed for yesterday of a serious sexual offence against a boy of 13, Tobin "totally denied being a danger to young people".
Despite knowing his HIV positive status, Tobin did not use a condom, said the judge.
Sally Bennett-Jenkins, for the prosecution, had told the court that the boy was being given HIV tests which have so far proved negative.
Tobin was caught after police kept watch on a house in Peckham, south- east London, where he was lodging, and saw a string of boys calling at the address.
The court was told Tobin tried to involve himself in domestic situations where he had regular contact with children who might be vulnerable to his sexual advances.
After the case, Child Protection Unit officers described the traumatic effect of Tobin's attack and his condition on the boy. "He is now totally mixed up," they said.
The youngster's family have attended court on previous occasions and hurled abuse at Tobin, but they were not present yesterday to hear sentence.
Police said they were "extremely bitter" at what Tobin had done to their son.Reuse content