Automatic Data Processing said on Wednesday that it is investigating a system intrusion that likely impacted only one client.

The intrusion, which occurred on a non-payroll legacy platform that is no longer sold by ADP's benefits administration business, was detected by the company's security team during routine system monitoring, the payroll and business outsourcing company said.

ADP did not name the affected client, but said the client was from Workscape, a benefits administration provider it acquired last year. ADP said it immediately notified the client to make the client aware of the situation.

ADP is the latest among high-profile targets of cyber criminals. Sony, Citigroup and the International Monetary Fund have been affected by data breaches.

ADP has about 550,000 clients. It said it could not disclose any additional details on the security breach, as the incident is the subject of an ongoing law enforcement investigation.

John Ribeiro covers outsourcing and general technology breaking news from India for The IDG News Service. Follow John on Twitter at @Johnribeiro. John's e-mail address is [email protected]