Security experts warn users to be on the watch for targeted email attacks after a breach at a major marketing firm. Names and email addresses of a “subset of Epsilon clients” were accessed by hackers last week. Epsilon, which sent 6.5 billion messages in 2009, runs email marketing and customer loyalty campaigns for some of the country’s biggest banks, credit card companies and retailers. The addresses will also be invaluable to attackers playing in the high-stakes game of hacking major corporations, experts say.”]