July 17 (Reuters) - Clover Health Investments CLOV.O said in a regulatory filing on Friday that it detected unusual login activity on some of its information systems on July 4 and later found a hacker had gained access to three employee accounts through social engineering.

• The health insurer said the affected accounts belonged to non-managerial health plan employees who handled member visit scheduling and broker-facing sales work.

• These accounts could access some personal and protected health information, according to the company, but not corporate financial or claims systems.

• Clover began an investigation with external cybersecurity experts, took steps to contain the activity and notified law enforcement, it said.

• The investigation is ongoing and the company is still reviewing what information may have been accessed or taken. Clover believes its response curbed and ended the unauthorized access.

• It also said it does not believe the incident has had, or is likely to have, a material impact on its business, financial condition or results of operations.

• Clover is reviewing legal and regulatory requirements and will notify affected members if needed, it added.

• Clover Health Investments is a U.S. health insurer focused on providing Medicare Advantage plans and technology tools for doctors.