Thousands of businesses and consumers are putting themselves at risk each day by publicly revealing their email addresses on Twitter.

Websense monitored Twitter in January and found that users were publicly sharing email addresses connected with their inboxes, social media identities, and bank accounts – leaving them open to advanced social spear phishing attacks.

Social spear phishing attacks see criminals attacking harvested email addresses with information gleaned from monitoring users' Twitter conversations. Websense recommends that businesses update all acceptable use policies to warn employees of this threat.

Researchers found more than 11,000 email addresses were shared worldwide over a 24-hour period.

They also conducted geo-targeted searches and discovered that more than 30 email addresses were shared every hour in London.

Carl Leonard, Websense Security Labs comments: “Twitter users blindly think that email addresses are safe for public consumption. However, by publicly tweeting your email, you’re connecting it with your name, location and information on your social graph. Criminals can exploit this wealth of information by directing waves of highly targeted phishing attacks at individuals or businesses, masquerading as users’ friends or associates to encourage them to click on malicious links.”

“Together this collection of data can also allow criminals to compromise email accounts, paving the way for further malicious activity including accessing bank accounts, harvesting additional passwords and launching major spam campaigns.

“Businesses employing social media to communicate with customers need to consider ways to ensure that employees are protected from these new threats. Employers should re-evaluate acceptable use policies to discourage staff from sharing email addresses on Twitter.”

Gmail, Hotmail and many other free web-based email services are particularly under threat as cyber criminals can harvest social information on individuals via Twitter to break into these accounts. Business leaders, journalists and celebrities were all found to be publicly sharing this data.