Yahoo apologized yesterday after people using its e-mail service were prevented from sending messages about anti-Wall Street demonstrations over the weekend.

The company said that an external spam filter had blocked the messages but maintained that it was inadvertent. It said that the problem has since been resolved, though there may be some residual issues.

ThinkProgress, which first noticed the problem, posted the following video of someone being blocked from e-mailing a message inviting their friends to visit the "Occupy Wall St." campaign Web site.

After typing in to the text field a message suggesting a visit to the Occupywallstreet.org Web site for more on the protests, the system kicked back the following message:

Your message was not sent

Suspicious activity has been detected on your account. To protect your account and our users, your message has not been sent.

If this error continues, please contact Yahoo! Customer Care for further help.

We apologize for the inconvenience.

A spokeswoman for Yahoo said that the company had not purposely blocked the messages. She said Yahoo initially became aware on Sunday "that some folks sending e-mail were getting the weird bounceback" but that Yahoo has since taken steps to resolve the problem.

This story originally appeared on CBSNews.com.