Professional networking website LinkedIn may be investigated by the Irish Data Protection Commissioner's Office after some user passwords were compromised in a security breach.

Gary Davis, Ireland's deputy data-protection commissioner said the incident falls within the area that can be investigated under the agency's code of practice on data breaches.

"We are in ongoing contact with LinkedIn in relation to the matter," Davis said in an e-mail.

"I am not in a position to indicate how we will be progressing."

Irish privacy regulators can levy fines on electronic- communication providers and networks for data breaches, Mr Davis said.

Ireland polices LinkedIn's data security because its base for operations outside the US is in Dublin.

The company, based in Mountain View, California, apologised to customers in a blog post yesterday and said that its more than 160 million users will know if their accounts were affected because their passwords will no longer be valid.

"We take the security of our members very seriously," LinkedIn said in the blog post. The company cites security issues as a risk for investors in regulatory filings and disclosed as recently as last month that it experienced website disruptions and outages for reasons including "denial of service or fraud or security attacks."