Credit unions have been marketing themselves as fundamentally different from behemoths like Bank of America for a long time. Now, their message has finally met its moment.

Between the Occupy Wall Street movement and a nationally organized "Bank Transfer Day" on November 5th, more than 700,000 people have moved their accounts from big banks to their credit union competitors, according to the Credit Union National Association. Those people have brought with them $4.5 billion in assets.

As they say: when the sun is shining, make hay.

At a moment like this it may be tempting for credit unions to invest in exactly the kind of messaging that brought those new members in the first place. In other words, market the story of why credit unions are more personalized and more committed to the communities they serve than their larger competitors.

What credit unions should really invest in, however, isn't telling the same old story only louder. Instead, credit unions should focus on improving the one area where big banks have consistently outperformed them: online and mobile banking. Credit unions do many things well, but they have always lagged behind in providing great user experience, whereas big banks have been able to make massive investments - and some significant leaps forward. Now is the time to narrow the technology gap.

This doesn't have to be done all at once. Credit union websites can be revamped to have the "look and feel" consumers now expect. While a modest expense, this first step can make a huge difference in the way you are viewed by your new and existing customers. The last message you want to send now, particularly to the Millenials now signing up, is that you are behind the times and out of touch with their needs. Unfortunately, many credit union websites, with their text-heavy pages and byzantine menu systems, communicate exactly that.

The same goes for core services like vehicle loan applications, many of which are completed through unprofessional looking forms and pages or worse yet, a PDF the user is forced to download and print in order to fill out. These systems can usually be revamped and upgraded without the huge cost and time commitment that a full legacy migration would take.

Credit unions should recognize this moment for what it is - an investment opportunity. New members may have come for the message, but they're not going to stay without the smooth online and mobile user experience they've become accustomed to at the big bank they just left.