A growing list of companies – from retailers to hotel chains to financial firms – are involved after a massive data breach at marketing services firm Epsilon.

Companies have been notifying customers that their email addresses and names may have been compromised in the breach.

Household names such as Best Buy, Target and TiVo are affected as well as credit card firms including Chase, Citi, Barclays and Capital One.

If you are customers of any of these companies you will probably have received an email warning you to watch out for future emails and not to give out any personal information or click on suspicious links or attachments.

PC World has a handy Q&A on what steps you can take to protect yourself.

The incident highlights the fact that data breaches can affect any type of organization. It also reminds us of the risk businesses face from this threat.

The average organizational cost of a data breach increased to $7.2 million in 2010 and cost companies an average of $214 per compromised record up from $204 in 2009, according to a recent study by Symantec Corp and the Ponemon Institute.

That same study also found that for the second straight year organizations’ need to respond rapidly to data breaches drove the associated costs higher.

In 2010, companies that notified victims within one month of discovering the breach had a per-record cost of $268, up 22 percent from 2009. Companies that took longer paid $174 per record, down 11 percent.

This means that rapid response to data breaches is costing companies 54 percent more per record than companies that moved more slowly, the study said.

Check out related I.I.I. information on identity theft.