Q. Is there any Internet security threat if I only visit reputable sites?

Yes there is a threat even if you only visit ‘safe’ places.  You could get a virus through emails, which redirects your links from what you thought was a reputable site to a phony site.  Banner ads on a reputable site can be poisoned with popup windows or drive-by download code  that can infect your machine.

With Zero Day Java exploits, I recommend disabling Java from your Web browser now unless it is absolutely needed for specific websites

Keeping your Web browsing safe:

Install the antivirus program and antispyware program of your choice to do continuous scanning, and make sure you keep it up to date. https://computer-answers.ca/2012/computer-questions/windows-questions/q-what-is-the-best-anti-virus-program/

I recommend using Firefox, and not Internet Explorer, because Firefox does not have ActiveX which is a vector for malware to get into Windows machines.

Turn off popup windows in Firefox’s Options, and install the NoScript add-on http://noscript.net/getit

Always keep your Windows, web browser and Java software up to date – frequent patches are released to plug security holes.
http://www.pcworld.com/article/149298/10_quick_fixes_for_the_worst_security_nightmares.html

SecuniaPSI will scan and alert you to out of date software
http://www.bleepingcomputer.com/tutorials/tutorial174.html

Keep up to date
Whichever browser you use, update it to the most recent version and keep it updated, and block popup windows, update your web browser’s plugins, add-ons, Adobe Flash Player and Adobe Reader to the latest versions from the official sites only (do not run updaters or installers from unknown sites or from an email link).

I recommend that you do not install any more browser plug ins, add ons or search bars than you absolutely need.

Beware of software installers that piggyback browser toolbars or search bars into the installation.  Make sure that you check or uncheck the options as appropriate to prevent this additional software from opening.  Search companies make revenue from advertising when your searches are directed through their site, and they pay shareware companies to bundle their installers. So there is a lot of incentive for them to sneak the software onto your machine. Some of the search software is malware and extremely hard to remove.

Consider disabling Java or at least keep it completely up to date. A number of viruses, trojan horses and web drive-by downloads attack your system through vulnerabilities in Java.  https://computer-answers.ca/2012/computer-questions/windows-questions/new-java-based-trojan-attacks-mac-windows-and-linux/

Blocking popups in browsers – instructions vary a bit depending on the version of your browser:

Firefox: Go to “Tools” or the “Firefox > Options” drop down menu, and choose “Options…” then in that window click the “Content” tab, then check the “Block pop-up windows” checkbox. support.mozilla.org/en-US/kb/Pop-up%20blocker

New Internet Explorer: Go to the “Gear” or “Tools” menu icon (or hit Alt-X), choose “Internet Options”, then choose the “Privacy” tab, and check the “Turn on Pop-up Blocker” checkbox. windows.microsoft.com/en-US/Windows7/Internet-Explorer-Pop-up-Blocker-frequently-asked-questions

Older Internet Explorer: Go to “Tools,” then “Pop-up Blocker.” Click the “Turn On Pop-up Blocker” checkbox.

Older Internet Explorer in Win XP:  support.microsoft.com/kb/843016

Safari: Choose the “Safari” tab at the top of the window. Click on “Block Pop-Up Windows.”

Chrome: Go to the “Chrome” or “Wrench” menu icon. Choose “Preferences” or “Options”. Click “Under the Hood.” Under the “Privacy” heading, click the “Content Settings” button. Click “Pop-ups,” found in the menu on the left side of the page. Click the second radio button under “Pop-Up Settings” or the “Do not allow any site to show popups” radio button. support.google.com/chrome/bin/answer.py?hl=en&answer=95472

More resources
Spyware Blaster blocks the URLs of known malware sites from your browser www.pcworld.com/downloads/file/fid,23106/description.html

McAfee Site Advisor flags websites security risks as you browse: www.pcworld.com/downloads/file/fid,62594-order,1-page,1/description.html

MyW0t (Web of Trust) allows you to search for reviews of particular sites www.mywot.com/

Scamadvisor.com collects reports of domains which are connected with scams or unethical business practices.

More on browser security
www.jack-brennan.com/?page_id=15

General Computer Security tips
http://www.pcworld.com/article/149298/10_quick_fixes_for_the_worst_security_nightmares.html

http://www.pcworld.com/article/254369/10_commandments_of_windows_security.html

Blocking adult or other unwanted websites