SINGAPORE - A district judge on Thursday warned parents of letting their children surf the Internet unsupervised , when he sentenced an unemployed man to three years' jail for sexually abusing and threatening a teen.

Community Court Judge Mathew Joseph said the case was also a lesson for young people who go online and download mobile applications, and find themselves ensnared by people like Chock Soon Seng.

He said the court found the 37-year-old's offences very disturbing and his conduct deplorable.

Chock, who faced five charges, pleaded guilty to two counts of sexual abuse and one of criminal intimidation at his flat in Hougang Avenue 8 in February and March this year.

The court heard that the victim downloaded a mobile application, Jack'd, on his cellphone..

After he became a member, Chock sent him a message and found out that the student was turning 15 this year.

While chatting, Chock asked him if he wanted to try kissing and sex, but the victim said he was not ready.

Later, the teen went to Chock's home in February. Chock took him to his bedroom where he removed the boy's clothes and took pictures of him on his iPad.

Chock next asked the victim to touch his body but the teen said he did not know how to and was uncomfortable doing it. He carried the victim onto the bed and asked him to perform oral sex on him. The two took turns performing oral sex on each other.

After the victim had gone home, he realised felt that what he had done was wrong, and the sexual acts were not right and "disgusting".

Two weeks later, he ignored Chock's text message to meet up.

Chock threatened the victim on March 21, saying that he would post his naked pictures to his friends if he did not meet him. He also said he would wait for the victim outside his house. The victim felt alarmed and decided to inform his family members. He made a police report the next day.

Deputy Public Prosecutor James Chew highlighted aggravating factors, saying the offences were serious and disturbing and warranted a stiff sentence to protect the public, especially young victims that could be preyed on.

Chock had been jailed for 10 months in 2010 for two counts of attempted exploitation of a child. He was a school teacher at the time.

He could have been jailed for up to 10 years and fined for sexual penetration of a minor; fined up to $10,000 and jailed for up to five years for the obscene act; and jailed for up to two years and fined for criminal intimidation.