City of London police arrested a Sage Group (SGE.L) employee on Wednesday at Heathrow Airport on suspicion of conspiring to defraud the British software maker, police said in a statement.
The 32-year-old woman was arrested on suspicion of conspiracy to defraud in connection with an alleged fraud against the company. She was subsequently released on bail, the police said.
Earlier this week, the Newcastle-based company, one of Britain's biggest tech firms, said an internal login had been used to gain unauthorised access to some of the personal employee data of around 280 of its British customers.
Sage supplies accounting and other financial software to 3 million small and medium-sized business customers globally. Its payroll-processing software is used by more than half of Britain's companies, analysts estimate.
Sage is working to ascertain whether any data has actually been stolen, a source at the company said on Monday.
Following the arrest, Sage declined to comment other than to reiterate it was cooperating with the police investigation.
The police statement said she was a current Sage employee but provided no further details.
(The storyu was refiled to make clear the suspect has not been charged)
(Reporting By Eric Auchard, editing by David Evans)