I should preface this by stating that I do like the announce plugin concept of announcing builds to 3rd party services. Tbhat being said you really should not put your ids, passwords in any build.gradle such as:
username = 'twitterid'
password = 'twitterpsswrd'
Obviously you should not do that but use the environments config slurper pattern and define the twitter id and passwords in the init.gradle file stored in user.home/.gradle/ and call define loadconfiguration() and call it in the build.gradle file with of course using the $config.twitter.twitterid and $config.twitter.twitterpsswrd patterns.
Than you have a reasonable secure pattern if you intend to extend the announce plugin say to connect to a googlewave widget for example.