Mollom was created by Dries Buytaert and Benjamin Schrauwen, and launched to a few beta testers (including myself) in 2007. Mollom was acquired by Acquia in 2012.
The service worked generally well, with the occasional spam comment getting through. The stated reason for stopping the service is that spammers have gotten more sophisticated, and that perhaps means that Mollom needs to try harder to keep up with the ever changing tactics. Much like computer viruses and malware, spam (email or comments) is an arms race scenario.
But there is a problem with this combinationa: reCAPTCHA, like all modules that depend on the CAPTCHA module, disable the page cache for any form that has CAPTCHA enabled.
This is due to this piece of code in captcha.module:
// Prevent caching of the page with CAPTCHA elements.
// This needs to be done even if the CAPTCHA will be ommitted later:
// other untrusted users should not get a cached page when
// the current untrusted user can skip the current CAPTCHA.
Another alternative that we have been using that does not disable the page cache is antibot module.
To install the antibot module, you can use your git repository, or the following drush commands:
drush dis mollom
drush dl antibot
drush en antibot
Visit the configuration page for antibot if you want to add more forms that use the module, or disable it from other forms. The default settings work for comments, user registrations, and use logins.
Because of the above mentioned arms race situation, expect spammers to come up with circumvention techniques at some point in the future, and there will be a need to use other measures, be they in antibot, or other alternatives.