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You could get Cyber bullied this is when someone bully’s you over the internet, makes you feel unsafe or threatens you. People could harass you with pictures or videos which may include you in it.
If you go on holiday and you say you are then people could possibly rob your house so if your going on holiday you shouldn't post it somewhere people you don't know can see it or just don't tell anyone over the internet.

You can make your account safe by having a strong password, don't give out personal details, don't say how old you are and lock your account so only certain people can see it. Don't leave your self logged in people can delete your work or post things that you don't want them to post.

Hacking 

Keep your personal details to your self don't tell any one your password they might try to hack in to your account. The person/robot hacking your account might have a virus and might want to transfer it to your computer using a social network prevent this by not clicking on pop ups and change your password every so often.