+(defcustom mm-w3m-safe-url-regexp "\\`cid:"
+ "Regexp matching URLs which are considered to be safe.
+Some HTML mails might contain a nasty trick used by spammers, using
+the <img> tag which is far more evil than the [Click Here!] button.
+It is most likely intended to check whether the ominous spam mail has
+reached your eyes or not, in which case the spammer knows for sure
+that your email address is valid. It is done by embedding an
+identifier string into a URL that you might automatically retrieve
+when displaying the image. The default value is \"\\\\`cid:\" which only
+matches parts embedded to the Multipart/Related type MIME contents and
+Gnus will never connect to the spammer's site arbitrarily. You may
+set this variable to nil if you consider all urls to be safe."
+ :type '(choice (regexp :tag "Regexp")
+ (const :tag "All URLs are safe" nil))
+ :group 'mime-display)
+