Heartbleed hacks hit Mumsnet and Canada's tax agency
15 April 2014 Last updated at 06:30 BST
A leading UK site for parents and the Canadian tax authority have both announced they have had data stolen by hackers exploiting the Heartbleed bug.
Mumsnet, which says it has 1.5 million registered members, said that it believed that the cyber thieves may have obtained passwords and personal messages before it patched its site.
The Canada Revenue Agency said that 900 people's social insurance numbers had been stolen.
Rory Cellan-Jones reports.