The government has issued a new warning on cooking with microwave ovens, asking consumers to thoroughly cook frozen chicken dinners.

The warning comes after 32 people in a dozen states got sick by salmonella.

Microwaves cook unevenly, potentially leaving cold spots that can harbor dangerous bacteria such as listeria and e. coli. That means microwaving anything that includes raw meat -- thawed or frozen -- can mean problems.

Officials say another problem is that consumers may cook using directions for a microwave with a different wattage than their own.