The security deployed in and around that stadium is a joke. Remember that Euro final between England and Italy? Embarrassing. Also, I'm sure the same invader got on TWICE during one of our finals (the Watford game? L.
They said they've spent £5m just on security updates since, and had a massive operation last night with thousands of stewards.
Obviously compared to the Euros, and Madrid/Liverpool in Paris, anything above the whole stadium burning down is probably considered a success.