It's unclear exactly what happened, however, reached by email, Boris Veldhuijzen van Zanten said the company is looking into the situation. According to its website, Twitter Counter "provides statistics of Twitter usage and tracks over 14 million users...and sells featured spots on its website to people who want to gain more followers." If it was hacked, the problem only appears to have hit accounts linked to the tool, so your account is probably safe. Still, as always, now is a good time to reset your password, and double check any apps or services linked to your social media accounts -- if they get compromised, you do too.

Update: Twitter Counter tweeted confirming the hack, and says the attackers are no longer able to post via its customer's accounts.