Twitter required some users to reset their passwords on Tuesday after discovering that their log-in information may have been harvested via security-compromised torrent Web sites, the company said.

For years, a malicious hacker has been setting up file-sharing torrent sites that appear legitimate and then selling them to well-meaning buyers who want to own their own download site, explained Del Harvey, Twitter's director of trust and safety, in a blog post.

However, the sites are riddled with malware and backdoors that allow the malicious hacker to steal log-in credentials -- like e-mail addresses, usernames and passwords -- from users who sign up for them.

Since people often use the same log-in information for multiple sites, the hacker has been breaking into Twitter accounts and possibly other social networks.

Twitter started investigating after it noticed an uncharacteristic spike in followers for a couple of accounts in recent days. It prompted users in the follower list of these accounts to reset their passwords.

The main takeaway for Twitter users: "We strongly suggest that you use different passwords for each service you sign up for," Harvey wrote.