Airport wi-fi injected ad script

if (window.addEventListener) {
    window.addEventListener("load", AIALoadEvent);
} else {
    window.attachEvent("onload", AIALoadEvent);
}

function AIALoadEvent() {
    if (self == top) {
        setTimeout(AIADisplayADV, 2000);
    }
}
    
function AIADisplayADV() {
    var url = 'http://www.wiz.athensairport.gr/Styles/WizBanners.css?a=1'
    if (document.createStyleSheet) {
        try { document.createStyleSheet(url); } catch (e) { }
    }
    else {
        var css;
        css = document.createElement('link');
        css.rel = 'stylesheet';
        css.type = 'text/css';
        css.media = "all";
        css.href = url;
        document.getElementsByTagName("head")[0].appendChild(css);
    }

    var aiaProxybackgroundDiv = document.createElement('div');
    aiaProxybackgroundDiv.setAttribute("id", "aiabackgroundDiv");
    var aiaProxyCenterDiv = document.createElement('div');
    var aiaProxyFooterDiv = document.createElement('div');
    aiaProxyCenterDiv.setAttribute("id", "aiaAdvDiv");
    aiaProxyFooterDiv.setAttribute("id", "aiaAdvFooterDiv");
    aiaProxybackgroundDiv.style.cssText = 'opacity:0.8; background: #000; width: 100%; height: 100%; z-index: 16777270; top: 0; left: 0; position: fixed; ';
    aiaProxyCenterDiv.className = "aiawizADV";
    aiaProxyFooterDiv.className = "aiawizFooterADV";
    var xhr1, xhr2;
    try {
        if (typeof XMLHttpRequest !== 'undefined') {
            xhr1 = new XMLHttpRequest();
            xhr2 = new XMLHttpRequest();
        }

        if (xhr1) {
            xhr1.withCredentials = true;
            xhr1.open("GET", "http://www.wiz.athensairport.gr/handlers/WizBanners.ashx?pos=1", true);
            xhr1.onload = function() {
                if (xhr1.responseText.length > 0) {
                    aiaProxyCenterDiv.innerHTML = '<div><div><input style="line-height: 12px;height: 24px;width: 24px;font-size: 8pt;font-family: tahoma;margin-top: 1px;margin-right: 2px;position: absolute;top: 0;right: 0;color: black; background: white none repeat scroll 0% 0%;border-radius: 4px;" type="button" value="X" onclick="hideAiaAdv()"></div>' + xhr1.responseText + "</div>";
                    document.body.appendChild(aiaProxybackgroundDiv);
                    document.body.appendChild(aiaProxyCenterDiv);
                }
            }
            xhr1.send();
        }
        if (xhr2) {
            xhr2.withCredentials = true;
            xhr2.open("GET", "http://www.wiz.athensairport.gr/handlers/WizBanners.ashx?pos=2", true);
            xhr2.onload = function() {
            if (xhr2.responseText.length > 0) {
                aiaProxyFooterDiv.innerHTML = '<div>' + xhr2.responseText + "</div>";
                    document.body.appendChild(aiaProxyFooterDiv);
                }
            }
            xhr2.send();
        }
    } catch (e) { }
}

function hideAiaAdv() {
    var div1 = document.getElementById("aiabackgroundDiv");
    var div2 = document.getElementById("aiaAdvDiv");
    div1.style.display = 'none';
    div2.style.display = 'none';
}

This is an example of an script automatically injected by the Athens Airport Free Wifi on every none-https website.
It's injected at the very beginning of the .

Only solution: visit HTTPS websites only.