Payment processor Euronet Worldwide Inc said a small portion of its European business was the target of a criminal security breach late last year, sending its shares down as much 6 percent.

The hacking of the system, which was revealed on Monday through a regulatory filing, affected a part of Euronet's processing business that accounts for less than 5 percent of its revenue, profit and transactions, the company said.

It was brought to our attention by the card organizations, Euronet Chief Executive Michael Brown told Reuters by phone.

When we heard the first little inklings of this, we jumped in, figured it out, got third parties involved who are real experts at this, and closed the breach... between our discovery and our shutdown, it wasn't a long period of time.

About the delay in disclosing the incident, Brown said it was not a severe breach.

Maybe the reason a lot of people didn't make a big deal about it, is just because the severity wasn't as bad as some other people have seen...We had a limited amount of bad activity and we've been free and clear for over a month, Brown said.

Expenses from the breach were less than 1 cent per share in the fourth quarter of 2011.

No claims or losses were asserted against the company in the fourth quarter 2011, Kansas-based Euronet said.

The company said it was working closely with international card associations and law enforcement agencies, but declined to comment if customers' personal data was stolen in the breach.

Several companies including Citigroup, Sony's Playstation network and Alliance Data's Epsilon unit were targets of hacking attacks last year.

Shares of the company closed at $18.23 on Monday on the Nasdaq.

(Reporting by Brenton Cordeiro in Bangalore; Editing by Sriraj Kalluvila and Gopakumar Warrier)