A man, smitten by his grandmother's neighbour, stalked the married woman from November 2016 to June 2017.
Technician Mohamed Sharizad Mohamed Samsuri, 37, tracked her down on Facebook and, posing as one of her friends, duped the 38-year-old into giving him her mobile phone number.
This led to a string of threatening WhatsApp text messages after she ignored his lewd messages asking for sex.
Yesterday, Sharizad was sentenced to 19 weeks in jail after pleading guilty to a harassment charge.
He also admitted to an unrelated charge of possessing more than 700 video files from pornographic websites.
District Judge Marvin Bay, in sentencing him, noted the steady escalation of his criminal behaviour.
It went "from his rather benign beginnings where he had extended invitations to add the victim as a friend on Facebook... to direct salacious messages, and then finally to utterly lewd requests for her to perform acts of fellatio on him... with overt sinister threats to expose her images and identity on social media", said the judge.
The court heard that the woman lived in the same block of flats as Sharizad's grandmother.
The location was not given in court documents.
Sharizad had spotted the victim after she moved into a unit there in 2009.
When he failed to get her attention, he turned to Facebook in early November 2016, and created multiple fake Facebook accounts under different pseudonyms, Deputy Public Prosecutor Vincent Ong told a district court earlier this year.
Sharizad used one of them to try to befriend her, but she ignored his request.
He then pretended to be her friend on Facebook and deceived her into giving out her mobile phone number.
In May 2017, he began harassing her, by calling her phone multiple times.
The following month, he sent her multiple threatening messages on WhatsApp.
In one of them, he enclosed a picture of the woman which he had taken earlier and stated: "Don't block me... or (you will) regret it."
The victim made four police reports in 2016 and 2017.
He was arrested and admitted to the offences on May 2, 2018.
Police later seized various devices from him, including two laptop computers where they found the obscene videos.