It's important to think about security when playing bingo games online. It's not that all bingo sites are insecure or trying to get your credit card details to commit fraud or steal your identity. That is no more true than saying that everyone you pass on the street would like to steal your handbag. Most websites offering bingo are perfectly legitimate but that is no reason not to be cautious. You wouldn't leave your purse on a table unattended and nor should you give your credit card details out to just anyone.
Most bingo sites will want your credit card details both so you can make payments and cash in any prizes you win. They might ask in advance, even when offering a free signup bonus or some free play for new registrants. In most cases that is just because customers are more likely to stay with a particular service provider if they have already given their card details, nothing sinister.
One way to make sure that websites with bingo games on them are legitimate is to choose the big names you know and have seen advertised on television, on radio, or elsewhere. These websites must have the financial backing to advertise and they wouldn't bother doing that if they were only looking to make some quick money off unwary people.
Some online games are run by the same people who own chains of bingo halls. If you're moving from playing bingo in the real world to playing online it's often possible to stay with a name you already know and trust. Another way to assess the quality of bingo sites is to look at which other websites link to them. It's a little like getting a recommendation from a friend. If a website you know to be reputable links to another site, then that site is probably a good one too.