Abuse FAQ for webmastersHow to limit network abuse HTTrack Website Copier FAQ (updated - DRAFT) Q: How to block offline browsers, like HTTrack? A: This is a complex question, let's study it First, there are several different reasons for that Why do you want to block offline browsers? : 1. Because a large part of your bandwidth is used by some users, who are slowing down the rest 2. Because of copyright questions (you do not want people to copy parts of your website) 3. Because of privacy (you do not want email grabbers to steal all your user's emails) 1. Bandwidth abuse: Many Webmasters are concerned about bandwidth abuse, even if this problem is caused by a minority of people. Offline browsers tools, like HTTrack, can be used in a WRONG way, and therefore are sometimes considered as a potential danger. But before thinking that all offline browsers are BAD, consider this: students, teachers, IT consultants, websurfers and many people who like your website, may want to copy parts of it, for their work, their studies, to teach or demonstrate to people during class school or shows. They might do that because they are connected through expensive modem connection, or because they would like to consult pages while travelling, or archive sites that may be removed one day, make some data mining, compiling information (“if only I could find this website I saw one day..”). There are many good reasons to mirror websites, and this helps many good people. As a webmaster, you might be interested to use such tools, too: test broken links, move a website to another location, control which external links are put on your website for legal/content control, test the webserver response and performances, index it.. Anyway, bandwidth abuse can be a problem. If your site is regularly “clobbered” by evil downloaders, you have various solutions. You have radical solutions, and intermediate solutions. I strongly recommend not to use radical solutions, because of the previous remarks (good people often mirror websites). In general, for all solutions, the good thing: it will limit the bandwidth abuse the bad thing: depending on the solution, it will be either a small constraint, or a fatal nuisance (you'll get 0 visitors) or, to be extreme: if you unplug the wire, there will be no bandwidth abuse 1. Inform people, explain why (“please do not clobber the bandwidth”) Good: Will work with good people. Many good people just don't KNOW that they can slow down a network. Bad: Will **only** work with good people How to do: Obvious - place a note, a warning, an article, a draw, a poem or whatever you want 2. Use “robots.txt” file Good: Easy to setup Bad: Easy to override How to do: Create a robots.txt file on top dir, with proper parameters Example: User-agent: * Disallow: /bigfolder 3. Ban registered offline-browsers User-agents Good: Easy to setup Bad: Radical, and easy to override How to do: Filter the “User-agent” HTTP header field 4. Limit the bandwidth per IP (or by folders) Good: Efficient Bad: Multiple users behind proxies will be slow down, not really easy to setup How to do: Depends on webserver. Might be done with low-level IP rules (QoS) 5. Prioritize small files, against large files Good: Efficient if large files are the cause of abuse Bad: Not always efficient How to do: Depends on the webserver 6. Ban abuser IPs Good: Immediate solution Bad: Annoying to do, useless for dynamic IPs, and not very user friendly How to do: Either ban IP's on the firewall, or on the webserver (see ACLs) 7. Limit abusers IPs Good: Intermediate and immediate solution Bad: Annoying to do, useless for dynamic IPs, and annoying to maintain.. How to do: Use routine QoS (fair queuing), or webserver options 8. Use technical tricks (like javascript) to hide URLs Good: Efficient Bad: The most efficient tricks will also cause your website to be heavy, and not user-friendly (and therefore less attractive, even for surfing users). Remember: clients or visitors might want to consult offline your website. Advanced users will also be still able to note the URLs and catch them. Will not work on non-javascript browsers. It will not work if the user clicks 50 times and put downloads in background with a standard browser How to do: Most offline browsers (I would say all, but let's say most) are unable to “understand” javascript/java properly. Reason: very tricky to handle! Example: You can replace: <a href=“bigfile.zip”>Foo</a> by: <script language=“javascript”> <!-- document.write('<a h' + 're' + 'f=“'); document.write('bigfile' + '.' + 'zip”>'); // --> </script> Foo </a> You can also use java-based applets. I would say that it is the “best of the horrors”. A big, fat, slow, bogus java applet. Avoid! 9. Use technical tricks to lag offline browsers Good: Efficient Bad: Can be avoided by advanced users, annoying to maintain, AND potentially worst that the illness (cgi's are often taking some CPU usage). . It will not work if the user clicks 50 times and put downloads in background with a standard browser How to do: Create fake empty links that point to cgi's, with long delays Example: Use things like <ahref=“slow.cgi?p=12786549”><nothing></a> (example in php:) 10. Use technical tricks to temporarily ban IPs Good: Efficient Bad: Radical (your site will only be available online for all users), not easy to setup How to do: Create fake links with “killing” targets Example: Use things like <a href=“killme.cgi”><nothing></a> (again an example in php:) <?php // Add IP. add_temp_firewall_rule($REMOTE_ADDR,“30s”); ?> function add_temp_firewall_rule($addr) { // The chain chhttp is flushed in a cron job to avoid ipchains overflow system(“/usr/bin/sudo -u root /sbin/ipchains -I 1 chhttp -p tcp -s ”.$addr.“ --dport 80 -j REJECT”); syslog(“user rejected due to too many copy attemps : ”.$addr); } |
我的书签
添加书签
移除书签
