Nokia has committed to monthly security updates for their phones, which means that the Nokia 6, the Nokia 5, and the Nokia 3 will all get these updates on a monthly basis and users of each of these devices can expect to see them at some point each month, and be assured that their devices will be just as secure as other Android phones and tablets in regards to vulnerabilities. Nokia mentioned the details about monthly security update in a tweet response to another user asking about the time frame of updates. They don't mention the Nokia 3, Nokia, 5, and Nokia 6 specifically, but those are the only Android devices they offer right now so it's logical that these are the devices they're referring to.
What is worth considering is that Nokia chose not to mention these three phones by name, and instead they stated that their products would support the security patch each month, which suggests that they'll be applying the patches to their future Android devices on a monthly basis as well. In addition to the security patches, Nokia's products will receive Android updates as well, though they do not mention any sort of time frame for this type of software update, so users will just have to wait until the company is likely ready to share more information on that in particular. That being said, all three of their current Android smartphones already have Android 7.1.1 Nougat installed, so they're already off to a great start when it comes to the software version that they're distributing with their devices, and hopefully for consumers who choose to pick one of their phones over another option, the attention to detail on software updates continues.
While the Nokia 3 and Nokia 5 are not yet available for purchase, the Nokia 6 was launched in China at the tail end of last year and is already doing well. Nokia did bring all three phones to Mobile World Congress last month to show them off too, though these seemed to be getting less attention than the only non-smartphone they had on display, the reboot of the Nokia 3310, which is an iconic phone in the world of cellular-connected mobile devices.