Let me deal with the first question to start with. LinkedIn faced attacks from hackers multiple times but recovered quickly. Making a blanket statement that they are safe will be overambitious and no platform today can guarantee full security.
When no one is at home you close entries with locks to secure your home similarly LinkedIn helps you with some preventive measures to secure your account.
The top three steps that come to my mind are
#1 Turn on Two steps verifications. You will receive an SMS alert if anyone tries unauthorized entry into your account. Unless you share the unique authentication code as a second layer of security generated by an app on your phone, no one can enter your account. This works well for me.
#2 Avoid using a Kiddish password. Since I mostly forget the password, I used the easiest one to recall it quickly. Many uses birthdates, mobile numbers, etc, as passwords. I have learned it hard way and started using a strong password with at least 10 characters including special ones, capital letters, numbers, etc that can save you greatly from hackers. Please use password stores to access it if you have forgotten.
#3 Fall for a Free PDF or a Gift. Most hackers use these methods to lure their victims. Not every link is vicious and robs your details but avoid sharing your emails and other credentials as these can expose you to hacking. Hackers share alluring links to access your bonus, gifts, or PDFs, these are potential traps to maliciously access your account. Please avoid those lures unless you know the source and are sure of the authenticity.
Now let me deal with the second part of your question. LinkedIn usage by employers has grown manifold in the last three years. Most companies prefer hiring through LinkedIn as they get much more sense than finding talent on regular job boards. I do have a recruiter’s account with them.
Once you apply, your resume goes to the recruiter. There are fake jobs everywhere, if you do some research on the company and study the vacancy advert, you may identify the Fake Jobs.
Most fake jobs put an unbelievable salary rather than talking about the details of the job. You may find multiple indicators like this and avoid those jobs.