It said
Dear Member,

As part of our efforts to provide a safe and secure environment for the online community, we regularly screen account activity.
Our review of your account has identified an issue regarding its safe use.
We have placed a restriction on your account as a precaution.

To lift the restriction we will require some further information from you.

If, once we review your further information and we're confident that the use of your account does not present a safety risk to our service and customers, we'll be happy to reinstate your account.

We have sent you an attachment which contains all the necessary steps in order to restore your account access.
Download and open it in your browser.
After we have gathered the necessary information, you will regain full access to your account.

We thank you for your prompt attention to this matter.

Very sincerely,

Halifax Online Services UK Review Department