The Heartbleed Bug is a serious vulnerability in the popular OpenSSL cryptographic software library which may have exposed users' personal information and passwords to hackers for the past two years.
Half a million sites are thought to have been affected.
IBM have put out a news alert stating "IBM Notes and Domino are not vulnerable to the Heartbleed bug because they do not use OpenSSL as the basis of the SSL stack in the products."
For more information on the Heartbleed bug, including a Q&A, go to http://www.heartbleed.com.