Users Cannot browse but can after reboot intermittant

[teqmod]

I have an office of about 250 users. We use a proxy server for access to the outside world which is controlled by a parent company. I have had several users complain they cannot browse the internet randomly. I have checked their browser settings and all is correct. restarting the browser does nothing. the browser never prompts for user/password but the machine is able to ping the proxy and other users work fine when the issue happens. It is not browser specific, happened to users with IE7 and IE8. I have confirmed all settings for hte proxy. A simple reboot does fix it but this seems to be happening more and more and when it has happened to the VP twice in a week we want to get it fixed. No Malware found and no viruses found on the machines that have had the issue so far. Has anyone experienced this or have any ideas where to go from here?

 

[kjv1611]

Some possible thoughts:

First, find every bit of info/data you can all all reported/affected machines to the best of your ability. Compare that with a handful of seemingly not affected machines. You should find a difference somewhere - diff piece of software, different usage methods, etc...

My first guess was their password had been locked, but as you mentioned no password prompts, I suppose that wouldn't be it.

When you say no malware/viruses found, how have you verified that? What programs/methods used for scanning?

 

[teqmod]

So far we have several machines, one in the finance department, two in the marketing department and 5-6 on the production floor. Unfortunately I have not found any software unique to these machines. They are even using different versions of IE. One is a windows 7 machine and the rest are XP. I have ran scans using Trend Micro AV and Malware Bytes with nothing coming up.

 

[kjv1611]

What about other applications? Do they all possibly have some similar applications? I'd want to take a list of the software installed on all of the affected machines, and compare to other machines, not affected, to see if any differences there.

 

[teqmod]

I have listed the software on the machines and not found any software unique to these machines. All of the finance machines have the same applications on them. I ran a utility on each of the machines as well as some of the other machines and there is nothing standing out.

 

[kjv1611]

Maybe they all ate their Wheaties with coffee in the bowl instead of milk, and then used the new-found energy, channeled it toward the computers, and fried some circuits?