Q Many websites that I’ve used don’t require you to type “www” on the front of a Web address. But when I used both the Firefox and Internet Explorer browsers to reach to one of the tinyurl.com websites in your column (without using the www), I got a “500 Internal Server Error” message. When I put the “www” prefix in front of the Web address, I still got the error, but on a second try I got connected. What’s the issue here?

Dennis Ciesielski, Menomonie, Wis.

A I don’t think using the “www” prefix had anything to do with it. The error message you received refers to a problem with the website’s server, and most of the time there’s nothing you can do. However, such website problems are often resolved quickly, so by retrying the Web address you probably reached the server when it was working again. But to make sure your browser isn’t contributing to the problem, clear its cache (the copies of Web pages it stores) and delete its cookies (bits of code that websites place in your browser so that you can be identified when you return.) To clear the cache in Firefox, see tinyurl.com/m6pngn5. To erase cookies in Firefox, see tinyurl.com/btt65bu. To clear the cache and the cookies in Internet Explorer, see tinyurl.com/lmt4nju.

Q Two different Web browsers on my computer have had their home pages hijacked by something called “Nation Zoom.” I’ve removed it from the browser settings only to have it reappear later. How can I remove “Nation Zoom”?

David Danielson, Orono

A Several steps are required. First, uninstall the Nation Zoom program from Windows. Then remove the virus from your browser by eliminating any “add-ons” (if you are using Microsoft Internet Explorer) or “extensions” (if you are using Google Chrome or Mozilla Firefox). Then remove Nation Zoom’s search engine from your browser and restore your proper home page. For instructions, go to tinyurl.com/l8m3cg2 and scroll down to “Manual Nation Zoom Search virus removal.”

Q I use two e-mail accounts when I’m in Miami, one through Comcast and the other through my Canadian Internet service provider. The Comcast account works, but the Canadian account can only receive messages, not send them. Comcast says this is because I’m using its network to reach both e-mail accounts, and it blocks e-mail transmission port 25, which my Canadian Internet service provider uses. Why is this happening?

Norm Shacter, Miami

A Comcast and several other large e-mail providers block “port 25,” an old e-mail transmission channel with limited security capabilities that’s used by troublemakers to send spam and malicious software. By blocking port 25, Comcast shuts out much undesirable traffic. Your Canadian Internet service provider should do the same.

E-mail tech questions to steve.j.alexander@gmail.com or write to Tech Q&A, 425 ­Portland Av. S., ­Minneapolis, MN 55488. Include name, city and telephone number.