You don’t get hacked just because someone knows your IP address – you get hacked if your machine has malware on it or if you have left services open to the public or if someone has obtained the username and password to your online accounts.
If you have properly updated firewall and anti-malware protection on, up to date Windows and applications, a strong WiFi password that you change regularly, and your router has a good Administrative password for its settings (read the router’s owner’s manual for instructions), then don’t worry about someone entering your machine.
Use strong passwords (combinations of letters and numbers, not dictionary words or easily guessed things like a pet’s name) for your online accounts, and change them regularly. http://www.microsoft.com/security/online-privacy/passwords-create.aspx
You can change a WAN IP address that your broadband modem uses to connect with your ISP. Most residential users have a dynamic IP address, if you turn off your router and your broadband modem for half an hour, you will most likely be assigned a new WAN IP by the ISP when you power back on. If you have changed that address, there is no way that the person with your old IP address knows what new address your outside network connection is at.
You need to be realistic about how people can ‘hack’ you. It’s not like television where people can enter your machine or smartphone in three seconds and take it over. If you have your machine properly secured and haven’t left ports and services open to the outside (like remote access, ftp or web server, and any kind of file, printer or connection sharing), then there is no practical way someone can ‘hack’ your machine.
One thing for sure, do not visit a website, download or install anything that an unknown person tells you to do, whether in a pop up screen, over the phone or by email. Remember, if you install something yourself which turns out to be malware, you have invited it past all of your firewalls and security, www.computer-answers.ca/2012/internet-networking/q-someone-called-me-from-my-internet-provider-and-told-me-my-machine-needed-to-be-fixed/
10 Windows 7 security steps www.pcworld.com/article/254369/10_commandments_of_windows_security.html
Windows 7 Checklist windows.microsoft.com/en-us/windows7/Security-checklist-for-Windows-7
Web security www.computer-answers.ca/2011/internet-networking/q-is-there-any-internet-security-threat-if-i-only-visit-reputable-sites/