diff --git a/Gemfile b/Gemfile
index 54dde2e8..36634fb0 100644
--- a/Gemfile
+++ b/Gemfile
@@ -18,6 +18,7 @@ gem 'tilt'
 gem 'erubis'
 gem 'stripe', :git => 'https://github.com/stripe/stripe-ruby'
 gem 'screencap'
+gem 'cocaine'
 
 platform :mri do
   gem 'magic' # sudo apt-get install file, For OSX: brew install libmagic
diff --git a/Gemfile.lock b/Gemfile.lock
index 60c6c663..e730f3ae 100644
--- a/Gemfile.lock
+++ b/Gemfile.lock
@@ -10,6 +10,12 @@ GIT
 GEM
   remote: https://rubygems.org/
   specs:
+    activesupport (4.1.4)
+      i18n (~> 0.6, >= 0.6.9)
+      json (~> 1.7, >= 1.7.7)
+      minitest (~> 5.1)
+      thread_safe (~> 0.1)
+      tzinfo (~> 1.1)
     addressable (2.3.6)
     ago (0.1.5)
     ansi (1.4.3)
@@ -30,7 +36,11 @@ GEM
       minitest (>= 2)
     celluloid (0.15.2)
       timers (~> 1.1.0)
+    climate_control (0.0.3)
+      activesupport (>= 3.0)
     cliver (0.3.2)
+    cocaine (0.5.4)
+      climate_control (>= 0.0.3, < 1.0)
     coderay (1.1.0)
     columnize (0.3.6)
     connection_pool (2.0.0)
@@ -168,11 +178,14 @@ GEM
     sinatra-xsendfile (0.4.2)
       sinatra (>= 0.9.1)
     slop (3.5.0)
+    thread_safe (0.3.4)
     tilt (1.4.1)
     timers (1.1.0)
     treetop (1.4.15)
       polyglot
       polyglot (>= 0.3.1)
+    tzinfo (1.2.2)
+      thread_safe (~> 0.1)
     unicorn (4.8.2)
       kgio (~> 2.6)
       rack
@@ -193,6 +206,7 @@ DEPENDENCIES
   bcrypt
   capybara
   capybara_minitest_spec
+  cocaine
   erubis
   fabrication
   faker
diff --git a/app.rb b/app.rb
index 5409544b..290888ec 100644
--- a/app.rb
+++ b/app.rb
@@ -636,7 +636,7 @@ post '/site_files/upload' do
     end
 
     if !Site.valid_file_type? file
-      file_upload_response "#{file[:filename]}: file type is not allowed on Neocities, upload cancelled."
+      file_upload_response "#{file[:filename]}: file type (or content in file) is not allowed on Neocities, upload cancelled."
     end
   end
 
@@ -941,7 +941,7 @@ post '/api/upload' do
 
   files.each do |file|
     if !Site.valid_file_type?(file)
-      api_error 400, 'invalid_file_type', "#{file[:filename]} is not a valid file type, files have not been uploaded"
+      api_error 400, 'invalid_file_type', "#{file[:filename]} is not a valid file type (or contains not allowed content), files have not been uploaded"
     end
   end
 
diff --git a/models/site.rb b/models/site.rb
index 9c3fc3b8..23301977 100644
--- a/models/site.rb
+++ b/models/site.rb
@@ -60,6 +60,12 @@ class Site < Sequel::Model
   SCREENSHOT_RESOLUTIONS = ['235x141', '105x63', '270x162', '37x37', '146x88', '302x182', '90x63', '82x62', '348x205']
   THUMBNAIL_RESOLUTIONS  = ['105x63', '90x63']
 
+  CLAMAV_THREAT_MATCHES = [
+    /^VBS/,
+    /^PUA.Win32/,
+    /^JS.Popupper/
+  ]
+
   BANNED_TIME = 2592000 # 30 days in seconds
 
   TITLE_MAX = 100
@@ -261,9 +267,26 @@ class Site < Sequel::Model
   def self.valid_file_type?(uploaded_file)
     mime_type = Magic.guess_file_mime_type uploaded_file[:tempfile].path
 
-    return true if (Site::VALID_MIME_TYPES.include?(mime_type) || mime_type =~ /text/) &&
-                   Site::VALID_EXTENSIONS.include?(File.extname(uploaded_file[:filename]).sub(/^./, '').downcase)
-    false
+    return false unless (Site::VALID_MIME_TYPES.include?(mime_type) || mime_type =~ /text/) &&
+                        Site::VALID_EXTENSIONS.include?(File.extname(uploaded_file[:filename]).sub(/^./, '').downcase)
+
+    File.chmod 0640, uploaded_file[:tempfile].path
+    line = Cocaine::CommandLine.new(
+      "clamdscan", "-i --remove=no --no-summary --stdout :path",
+      expected_outcodes: [0, 1]
+    )
+
+    output = line.run path: uploaded_file[:tempfile].path
+
+    return true if output == ''
+
+    threat = output.strip.match(/^.+: (.+) FOUND$/).captures.first
+
+    CLAMAV_THREAT_MATCHES.each do |threat_match|
+      return false if threat.match threat_match
+    end
+
+    true
   end
 
   def store_file(filename, uploaded)