Jobseekers are being warned that fraudsters could be using fake online recruitment adverts to persuade people to hand over personal information which can then be used to scam them.

The Office of the Privacy Commissioner for Personal Data (PCPD) on Thursday said people should not provide details like their ID card numbers if responding to "blind ads", where the identity of those behind the post is not clear.

Privacy Commissioner Ada Chung said her office checked more than 22,000 recruitment adverts across 13 online platforms and found 23 blind ads from June to September this year.

"I would advise jobseekers to be careful and to be vigilant about blind ads because they need to find out who is the employer in question, and they should try to ascertain and verify the information contained in the blind ads carefully before they submit any personal data," Chung said.

"The blind ads may be used by fraudsters to perpetuate fraud, and it is actually very risky for them [jobseekers] to submit their personal data in such circumstances."

Chung also advised employers to disclose their identity when placing adverts.

"They should also refrain from placing blind ads to collect job applicants' personal data. If necessary, they should consider engaging a recruitment agency who is identified in the advertisement to collect personal data from jobseekers," she said.

"I think it is to the advantage of the employer as well because it will project a positive corporate image."

Chung said the PCPD has started investigations into five organisations that have placed blind ads.