Okay so a lot of folks are being affected by these bots, pain in the ass I know
#1 So first of all if you would like to prevent these altogether, change your privacy settings to only allow messages from friends(this will prevent messages from other gamers that aren't on your friends list)
#2 You can do the service a favour and finish their scripts, to do this, type 5 characters or more and send in return to the bots messages until the bot replies with a message simply with the letter "a" in it, you have now finished the bots script
Then report the message with the link in it from the bot, report it under the category "message" add a comment to the report saying "porn bot"
The more messages MS have to work with the faster they can compile all the scripts to set up a spam filter on them
#3 if you don't have the time and they're a pain in the ass and still want to communicate with other members you meet online, simply block the account