安装firefox的QQ插件后访问arxiv出现问题
前几天去下了别人的qq中转站的几部电影，有些链接出现问题，安装了2个firefox插件：QQ旋风和QQ storage。
后来就出现访问不了arxiv.org的问题，界面提示403 Forbidden:
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Access Denied
Sadly, your client "Mozilla/5.0 (Windows; U; Windows NT 5.1; zh-CN; rv:1.9.1.7) Gecko/20091221 Firefox/3.5.7 QQDownload/1.7" violates the automated access guidelines posted at arxiv.org, and is consequently excluded.
If you believe this determination to be in error, see http://arxiv.org/denied.html for additional information.
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http://arxiv.org/denied.html的信息如下：
Access Denied
Accesses from your site have triggered our automatic robot detection system. (Sometimes a block is caused by another user from behind the same proxy.) For immediate access to arXiv, you may wish to use a mirror site instead.
The block may have been triggered by use of `accelerator' or pre-fetching software. You must remove or disable such software before accessing our site.
In the event that further assistance is needed, please report to (and only to) www-admin@arXiv.org, so your problem can be investigated. Note: You must report that the blocked access was logged from:
(none) [121.*.*.*] at arxiv.org
with User-Agent: Mozilla/5.0 (Windows; U; Windows NT 5.1; zh-CN; rv:1.9.1.7) Gecko/20091221 Firefox/3.5.7 QQDownload/1.7
(without this information your query will have to be ignored, and note that administrative time is very limited so not all queries can receive a rapid response in any event).
Thank you for your cooperation..
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把QQ插件全部卸载之后，还是保持不变，给arxiv.org去信问是否ip被封的问题，回我说：
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Your access is being denied because of your usage of the QQDownload user agent (which comes from the Tencent QQ instant messaging application). This software is prohibited, as it is associated with malware and is considered a security risk. You *must* uninstall or disable this software before you can access arXiv.org.
If you cannot or will not disable this software, you must utilize one of our mirror sites such as:
http://cn.arxiv.org
For a complete list of servers please see:
http://cn.arxiv.org/servers.
For more information about QQDownload, see:
http://en.wikipedia.org/wiki/
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但是访问http://cn.arxiv.org/还是出现那样的问题
用Total commander搜索c盘的"QQ donwload"然后删除相关文件，再把firefox的cookie全部清空，还是不行。
至始至终，用chrome或者IE或者搜狗浏览器都访问arxiv正常，不知道为什么。
2010-01-26更新：
今天继续google，在下面这个网址找到一种方案
http://snet.xznu.edu.cn/post/faq.html
关于arxiv上不去那个问题，这是腾讯超级旋风搞的鬼，把它删掉就好。如果用的是firefox，则还要找到firefox安装目录，比如我的是 firefox plus\data\，在这个文件夹下找到prefs.js文件，用记事本打开，搜索qqdown关键词，把对应的配置语句删掉。
我用total commander按alt+F7在c盘查找prefs.js，目录和上面不一致，而且有好几个prefs.js文件，只有C:\Documents and settings\user\application data\mozilla\firefox\profiles\btkhuc29.default\prefs.js目录下找到的prefs.js内含qqdown关键字，句子为
user_pref("general.useragent.override", "Mozilla/5.0 (Windows; U; Windows NT 5.1; zh-CN; rv:1.9.1.7) Gecko/20091221 Firefox/3.5.7 QQDownload/1.7");
删除后重新打开firefox还是失败，然后发现回到上面那个目录去重新看prefs.js文件，上面的这个句子又已经自动回复了。删除整个prefs.js文件仍然会自动生成，恢复如初。
继续google 如何修改prefs.js的帮助，找到问题所在“要想直接修改 prefs.js，应该完全关闭 Firefox（关闭所有的 Firefox 窗口）之後再打开 prefs.js 进行编辑，要不然编辑可能会被复盖。”
才发现自己确实没有在修改prefs.js的时候关闭firefox，赶紧按如上操作，问题终于恢复！
总结：
Q：firefox访问arxiv提示无法访问，出现有qqdownload软件/插件的威胁安全问题。
A：先卸载firefox的qq插件（主要是qq超级旋风下载插件），然后关闭firefox（这个一定要注意！），搜索整个c盘的prefs.js，用文本文件逐一打开查找关键词“qqdownload”，删除所在的整个句子，保存再关闭。然后重新打开firefox，再检查一遍prefs.js的qqdownload语句没有被恢复，再在firefox地址栏敲入arxiv.org测试连接。如果不行，请按这篇帖子重头到尾把其他操作加进来完整操作一遍。
