Is there any security impact on current org due to new release winter17? I would like to see difference between old release and new release. Can anyone please suggest me?
If you have a Production Org with sandboxes then you will have the sandboxes updated prior to the introduction of the release in live meaning that it is possible to do a regression test around your current setup which will allow security and customisation to be tested with the new release.
Ultimately this would have to be a Salesforce Org specific task as apart from general changes such as TLS1.0 being desupported and the Winter17 requirement for HTTPS for all logins it will depend on the features that you are using.
For example in Winter17 HTTPS is now required for all logins
Logging in to a Salesforce server instance, such as na1.salesforce.com, now requires an HTTPS secure connection. Previously, HTTPS was required for logins via login.salesforce.com and custom domain URLs. HTTPS is now required for all Salesforce logins. Replace HTTP with HTTPS any time you call yourInstance.salesforce.com. This feature is available in both Lightning Experience and Salesforce Classic.