Nonsense. Information Security (as it was called before "cyber" became the new black) is plagued by much more basic problems. For example that half of the companies in any given country basically don't have any. Or that we've still not solved basic problems like account enumeration or brute-force attacks (which, you wouldn't believe, way too many applications still allow).
There are essentially two games. The one is where baseline security is attacked, hackers looking for the weakest link, for targets of opportunity, and if you have adequate security, you're good. It's a case of not having to outrun the bear.
And then there are the target attacks on high-priority targets. Done by top-notch professional attackers, often backed by organised crime and/or nation states. Unless you have equally top-notch security, you're toast.
In both cases, Brexit or not makes little difference. In the first case, everything you need to know is in basically any "IS for dummies" guide. In the later case, the required information isn't shared by bureaucrats in Brussels, but by tech experts in conferences and informal meetings. Since the UK isn't part of the Schengen zone anyways, no difference in travel arrangements, Brexit or not.