She earlier denied one charge of conspiracy to commit buggery. She also faces an alternative charge of conspiracy to commit indecent assault.

Simon Tam Man-fai SC, for the prosecution, earlier told the court the woman knew the man, whom she had met online, was a paedophile, but she allowed her son to be molested for money. She also had sex with the man.

The prosecution said the woman took her son to the man's flat three times between April and September 2011. The assaults took place in the flat.

"Every time the defendant took the child to the man, she knew clearly the man would have sex with the boy," Tam earlier told the court.

"Every time, she took the boy there, she would put him on a drug to reduce the pain and let him forget what had happened."

The woman said she did not see the man molesting her son, but that on one occasion, she saw the boy, with his pants off, lying in bed with the man.

She said the pills the man fed her son were to help him sleep better because the boy did not sleep well at night.

She added that the man had been her sex partner since 2008, and that all their sexual contact involved money.

The court was told the boy had been born out of wedlock, and that the woman was currently living with her boyfriend.

The case came to light only when she resigned from her job last July.

Her employer - following company practice to delete former workers' MSN records - found 39 pages of dialogue between the mother and another party on topics about sex and having sex with a child.

The employer contacted the Social Welfare Department, which then referred the case to the police.

The trial continues today before a seven-member jury and Mr Justice Louis Tong Po-sun.