there could be a few basic spam prevention methods enabled by default

• site-wide post cooldown. after posting (and maybe commenting), you should have to wait some time to post again until you have a certain amount of "karma" or whatever it's called here and/or after a certain amount of time
• ip banning. im not sure if that info is even being recorded, but if it is it would probably be simple enough to implement. maybe that's too heavy-handed though
• another option is referral only signups, since that'll help trace down where the spam is coming from. unfortunately, at the same time, it would hurt the growth of the site