SHA is a popular hashing algorithm used by the majority of SSL certificates. As computing power has increased the feasibility of breaking the SHA1 hash has increased.
This usually means the implementation of SSL on your server is not correct. The error is usually caused by a server side problem which the server administrator will need to investigate.
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How to complete DNS authentication for RapidSSL, Geotrust or Thawte orders
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When you login to Servertastic you may receive an email (example below) informing you that your account could have been hacked, compromised or stolen.