She was not going to take it sitting down. Or in her case, standing on a crowded escalator in an MRT station.
The 22-year-old sales manager, who wanted to be known only as Miss Tan, sensed someone standing very close to her and realised the man was taking upskirt photos of her.
The man moved away quickly when she turned around.
Determined not to let him get away, she not only followed him into a train, but also managed to take a photo of him with her phone camera and called the police.
When the alleged pervert realised something was up, he bolted out at the next station.
But the resolute Miss Tan chased him and alerted SMRT officials, who detained the man until the police showed up.
She later told Lianhe Wanbao why she was so determined to get the man: "I was thinking at that moment that justice should be done and that the pervert should be punished."
Recounting the incident, which happened last month, Miss Tan said she was returning home from her workplace near Promenade station on the Circle Line in the evening.
When she arrived at Paya Lebar MRT station, she alighted and got on an escalator to transfer to the East-West line.
She suddenly sensed someone very close to her and "felt extremely uncomfortable".
When she turned around, she saw a man in his 30s holding a mobile phone with the camera facing upwards under her dress.
"He was flustered when he saw me turn around and quickly put his mobile phone back into his pocket," Miss Tan said.
"I pretended to be making a call to my friend and moved down the escalator so that I was behind him."
She then followed him into a train heading towards Pasir Ris.
"I stood not too far away from him and called the police to report him. I then used my mobile phone camera to capture his appearance."
When the man discovered that she had taken a photo of him, he dashed out of the carriage when the MRT train pulled into Bedok MRT station and ran down the stairs.
Miss Tan told Lianhe Wanbao: "He was running away while I chased him, and once I reached ground level, I banged on the door of the station control, pointing at the upskirt pervert while I asked for help from the SMRT officials.
"After around five minutes, the officials caught hold of him and hauled him back."
The man was detained at the MRT station control until three police officers arrived.
He was subsequently taken to a police station after Miss Tan related the incident to the officers.
The police confirmed that they received a call on June 12 at about 5.55pm requesting for assistance at Bedok MRT station.
They later arrested a man in relation to the case.
Miss Tan said she contacted the police on Tuesday for updates on the case and found out that the suspect had been released on bail pending investigations.
"I feel extremely uneasy, especially after I heard that he lives near my home. I'm afraid that I might bump into him," she said.
As a short-term measure, she will be returning home only once a week.
"For my safety, I've quit my job and got permission from my parents to move into my boyfriend's home," she said.