A 32-year-old employee at software firm Sage has been arrested at Heathrow airport, police have said.
City of London police said the woman was arrested on Wednesday in connection with a fraud investigation and has since been bailed.
Earlier this week the software firm was the victim of a data breach, which may have compromised personal information for employees at 280 UK businesses.
The Newcastle-based firm said it had told businesses who may be affected.
The firm provides business software for accounting and payroll services to firms across 23 countries.