You track your bank account regularly and make sure there are no unauthorized charges on your credit cards. But when did you last check your frequent-flier accounts?

Thieves are stealing miles and points and turning them into cash. Criminals gain access to your account and either sell or barter your miles and points online or redeem them for tickets, merchandise or gift cards. United changed its login procedures in August after some thefts around the industry. Other airlines say they are studying possible security enhancements.

Many consumers don’t protect their accounts with complicated passwords, or they use the same password at multiple sites. Airlines, hotels and others with loyalty programs have simple sign-in processes that experts say can be hacked.

Perhaps most important, lots of people don’t check their accounts very often, giving thieves a head start before anyone notices unauthorized withdrawals. Most airlines no longer mail out monthly account statements. They send electronic updates that are often ignored.

Thieves stole miles from thousands of accounts last year, including those belonging to United and American customers, after obtaining passwords from a chat-room site and using the same passwords to get into mileage accounts.