It is becoming increasingly difficult to protect a site from being hacked! Below are some lines which can be added to the .htaccess file to protect a site against some of the most common vulnerabilities:

# prevent access from santy webworm a-e
RewriteCond %{QUERY_STRING} ^(.*)highlight=\%2527 [OR]
RewriteCond %{QUERY_STRING} ^(.*)echr(.*) [OR]
RewriteCond %{QUERY_STRING}% s:(.*)252echr [OR]
RewriteCond %{QUERY_STRING} ^(.*)esystem(.*) [OR]
RewriteCond %{QUERY_STRING} ^(.*)rush=\%65\%63\%68 [OR]
RewriteCond %{QUERY_STRING} ^(.*)rush=echo [OR]
RewriteCond %{QUERY_STRING} ^(.*)wget\%20 [OR]
RewriteCond %{QUERY_STRING}% s:(.*)wget
RewriteRule ^.*$ http://127.0.0.1/ [R,L] 

# prevent pre php 4.3.10 bug
RewriteCond %{HTTP_COOKIE}% s:(.*):\%22test1\%22\%3b
RewriteRule ^.*$ http://127.0.0.1/ [R,L]  

# this ruleset is to "stop" stupid attempts to use MS IIS Web Server expolits on us
# NIMDA
RewriteCond %{REQUEST_URI} /(admin|cmd|httpodbc|nsiislog|root|shell)\.(dll|exe) [NC]
RewriteRule .* - [F,L]

# CODERED
RewriteCond %{REQUEST_URI} /default\.(ida|idq)$ [NC,OR]
RewriteCond %{REQUEST_URI} /.*\.printer$ [NC]
RewriteRule .* - [F,L]

# IE's "make available offline" mode
RewriteCond %{HTTP_USER_AGENT} MSIECrawler [OR]

# unknown bot
RewriteCond %{HTTP_USER_AGENT} ^NG [OR]

# You may want to enable these lines below to disallow php and perl scripts to access your site
 RewriteCond %{HTTP_USER_AGENT} ^.*PHP.*$ [OR]
 RewriteCond %{HTTP_USER_AGENT} ^.*libwww-perl [NC,OR]

# Ignorant user trying to edit my site
RewriteCond %{HTTP_USER_AGENT} FrontPage [OR]
#this one will ban everything microsoft. Use with caution.
RewriteCond %{HTTP_USER_AGENT} ^(Microsoft|MFC).(Data|URL|WebDAV|Foundation).(Access|Control|MiniRedir|Class) [NC,OR]

# MSOffice
RewriteCond %{REQUEST_URI} ^/(MSOffice|_vti) [NC,OR]

# Various
RewriteCond %{REQUEST_URI} ^/(bin/|cgi/|cgi\-local/|cgi\-bin/|sumthin) [NC,OR]
RewriteCond %{THE_REQUEST} ^GET\ http [NC,OR]
RewriteCond %{REQUEST_URI} /sensepost\.exe [NC,OR]
RewriteCond %{REQUEST_METHOD}!^(GET|HEAD|POST) [NC,OR]

# Cyveillance is a spybot that scours the web for copyright violations and ?damaging information? on
# behalf of clients such as the RIAA and MPAA. Their robot spoofs its User-Agent to look like Internet
# Explorer, and it completely ignores robots.txt. I have
# banned it by IP address.
RewriteCond %{REMOTE_ADDR} ^63\.148\.99\.2(2[4-9]|[34][0-9]|5[0-5])$ [OR]
RewriteCond %{REMOTE_ADDR} ^63\.226\.3[34]\. [OR]
RewriteCond %{REMOTE_ADDR} ^63\.212\.171\.161$ [OR]
RewriteCond %{REMOTE_ADDR} ^65\.118\.41\.(19[2-9]|2[01][0-9]|22[0-3])$ [OR]

# NameProtect peddles their ?online brand monitoring? to unsuspecting and gullible companies
# looking for people to sue. Despite the claims on their robot information page, they do not
# respect robots.txt; in fact, they spoof their User-Agent in multiple ways to avoid detection.
# I have banned them by User-Agent and IP address.
RewriteCond %{REMOTE_ADDR} ^12\.148\.196\.(12[8-9]|1[3-9][0-9]|2[0-4][0-9]|25[0-5])$ [OR]
RewriteCond %{REMOTE_ADDR} ^12\.148\.209\.(19[2-9]|2[0-4][0-9]|25[0-5])$ [OR]
RewriteCond %{HTTP_USER_AGENT} ^NPBot	[NC,OR]

# Web Content International
RewriteCond %{REMOTE_ADDR} ^65\.102\.12\.2(2[4-9]|3[01])$ [OR]
RewriteCond %{REMOTE_ADDR} ^65\.102\.17\.(3[2-9]|[4-6][0-9]|7[01]|8[89]|9[0-5]|10[4-9]|11[01])$ [OR]
RewriteCond %{REMOTE_ADDR} ^65\.102\.23\.1(5[2-9]|6[0-7])$ [OR]

# dumb bot
RewriteCond %{HTTP_USER_AGENT} "^Mozilla/4.0$" [OR]

# Wordtracker
RewriteCond %{REMOTE_ADDR} ^128\.242\.197\.101$ [OR]

# Unknown
# unknown.Level3.net
RewriteCond %{REMOTE_ADDR} ^64\.156\.198\.(6[89]|7[0-9]|80)$ [OR]

# host25x.keebler.com
RewriteCond %{REMOTE_ADDR} ^65\.223\.250\.25[0-3]$ [OR]

# Turnitin spybot
RewriteCond %{REMOTE_ADDR} ^64\.140\.49\.6([6-9])$ [OR]
RewriteCond %{HTTP_USER_AGENT} TurnitinBot [OR]

# this ruleset is for formmail script abusers...
# we don't use Perl for Postnuke so this is not really needed.
RewriteCond %{REQUEST_URI} (mail.?form|form|form.?mail|mail|mailto)\.(cgi|exe|pl)$ [NC,OR]
RewriteCond %{HTTP_USER_AGENT} ^.*FileHound.*$
RewriteRule .* - [F,L]

# dumb bot
RewriteCond %{HTTP_USER_AGENT} "^Mozilla/3.0$"
RewriteRule .* - [F,L]

<FILES .htaccess>
order allow,deny
deny from all
</FILES>