Prohibition orders have been issued against three Singaporean men who ran an illegal share trading scheme that netted them more than $2 million each.

The orders against former UOB Kay Hian representative Simon E Seck Peng and former First State Investments (Singapore) representative Leong Chee Wai are for 15 years.

Toh Chew Leong, also a former representative of First State Investments (Singapore), was given an order for 13 years by the Monetary Authority of Singapore.

The orders, which took effect from Tuesday, bar the men from any regulated activity under the Securities and Futures Act (SFA).

They are also banned from taking part in the management, acting as a director or becoming a substantial shareholder of any capital market services firm under the SFA.

The three men had colluded to misuse confidential information obtained in the course of their work for personal gain.

They were engaged in a "front-running" arrangement over seven years. Front-running involves a broker using advance information of pending share orders to place buy or sell trades through his personal account, with the aim of benefiting once the stock price moves.

Last month, the three men were convicted of insider trading offences and sentenced to jail terms ranging from 20 to 36 months. It was the first front-running case prosecuted as an insider trading offence, which attracts a heavier punishment, in part due to the involvement of price-sensitive information.

The case centred on offences committed between 2007 and 2014 that involved about 40 Singapore-listed companies, including Ascendas Real Estate Investment Trust, CapitaMalls Asia and Global Logistic Properties. Foreign-listed stocks were targeted as well.