Just a quick copy paste from a fishing forum where this came up
So as mentioned in the chat box by fishing forum website member they were warned the site was not secure all this warning was saying is there is no SSL encryption of informantion traveling from what you type in to the database where the site is hosted and then from the data base back to the poster or when you read the topic the veiwer.
The SSL is secure socket layer you may be used to seeing https in sites like your bank or google and such along with a little green lock that shows in the address bar showing it as a safe website but all that means is the owner of the webiste is paying extra for that encryption of information so people cant launch a man in the middle attack or basicly intercept the data on its way to where its going and be able to steal the information another version of this is the rayban ad's if you have been on facebook and have been tagged in 'cheap' ones that is what is happening because the link takes you to a false site where your data can be skimmed off and used to spread to more people.
If what i have posted has you worried easy ways to protect yourself are,
Dont use the same passwords twice.
Do have a anti virus installed and upto date.
Dont go to sites that offer things that are to good to be true.
Dont open those emails that ask you to go somewhere for a reward (Email places normaly spot these and send them to a folder called spam).
Hope this helps explain why there may be the unsecure alert.