Use a good spam filter plugin such as anti-spam... as well as captcha's on forms to prevent bots from implementing automated entries and finally be careful not to openly display your email address which can be scraped and used as part of spam emailing...
It depends on the type of captcha breaker... The best ones are the type where you either have to add some numbers or drag and drop an item based on a random question... In otherwords its much harder to overcome using software and requires a real person to get passed it...