Pharmaceuticals giant Pfizer has confirmed that it has suffered a huge data breach, its third in a year.

Personal information relating to as many as 34,000 of its staff has been harvested, presumably for use in identity theft.

The data was stolen by a former employee of the company last year, but Pfizer only found out about the breach in July.

"So far there is no indication that any unauthorised person has used or is misusing the information that was removed from Pfizer," said the company in a letter to its staff (PDF).

"Nonetheless, we want you to know now, and to have tools and information to help you prevent and detect any misuse.

"Pfizer has notified law enforcement and has retained Identity Safeguards, a specialist in identity theft protection, to provide you with two years of protection and restoration services free of charge."

This is the third data breach Pfizer has admitted to since June. The company said that it may have lost the details of 17,000 employees earlier in the year when peer-to-peer software was used on one of its machines.

In a separate incident in July two company laptops with staff details were stolen from a car.

The company is facing criticism for its slow response to the data breaches. Despite finding out about the attack in early July, staff were only told six weeks later that their information could have been compromised.