network/security issue on small company network

[$ReaPeR$]

Hey guys
A problem has occurred on the device network at my place of work, and since I'm the official technician, I'm in charge of dealing with it. Although my major was in networking, I have a very limited practical experience so this may well be a very stupid/easy problem to fix. Anyway, the problem is as follows.
There are 7 PCs connected to the network + a server, all the pc's show the following image when trying to load various pages in ie/chrome/firefox, the pages are unrelated to each other and they are "safe", it does it even when trying to load the "steam" homepage, but not on all computers, some of them load it normally. The pc's are usually used to browse porn. (due to the nature of the place) (sorry for my syntax/grammar, English is not my mother tongue)
Thank you in advance

 

[silentbogo]

Check client PCs with this issue for any similarities (same browser, same AV, any adblocker/security add-ons etc)
Check if there is any consistency between client IPs on which websites are being blocked (in case there is some long-forgotten firewall setting or anything of a kind running on your server). Re-check firewall settings on your server and see if there is any kind of URL or content blocking.
That's about all I can think of.

The pc's are usually used to browse porn.

Are you, guys, hiring?

 

[Kursah]

What are you guys using for security (anti virus, web filter, etc.)? That could be a web filter though usually there's a logo.

Are you guys using any kind of proxy?

Are you using a business-grade router/firewall for your gateway? Is it being properly maintained and support contracts renewed?

Have you changed ISP's or have they introduced DNS filtering security-related services (similar to OpenDNS)?

 

[$ReaPeR$]

Check client PCs with this issue for any similarities (same browser, same AV, any adblocker/security add-ons etc)
Check if there is any consistency between client IPs on which websites are being blocked (in case there is some long-forgotten firewall setting or anything of a kind running on your server). Re-check firewall settings on your server and see if there is any kind of URL or content blocking.
That's about all I can think of.


Are you, guys, hiring?

Thanks for the reply mate actually if u live in Copenhagen there might be a chance for that to the point tho.. all the pcs have this issue on all available browsers, all on win 7 64 bit except for one which is using win 10 pro 64 bit. nothing has been changen on the network, but the server did do some updates the last time i checked it, ie 2 days ago. you think that could be an issue?

What are you guys using for security (anti virus, web filter, etc.)? That could be a web filter though usually there's a logo.

Are you guys using any kind of proxy?

Are you using a business-grade router/firewall for your gateway? Is it being properly maintained and support contracts renewed?

Have you changed ISP's or have they introduced DNS filtering security-related services (similar to OpenDNS)?

also thank for the reply the router is home grade, and very weird i might add, its "made" by a local company but it seems to have a broadcom chip. also im not aware of any proxy, im the "new" guy and the previous fellow is not to be bothered so.. im on my own on figuring everything out..

 

[SamirD]

Porn sites are notorious for having malware and linking to other 'bad sites'. You're infected with something, and something strong. I would do nothing short of imaging all the systems if you have image backups. Otherwise, destroy and re-format and re-install everything.

And to prevent this type of thing in the future, I would highly encourage using something like deep freeze or reboot restore to keep the systems in a steady state. Better yet, use windows embedded thin clients and reboot daily.

 

[Solaris17]

Hey guys
A problem has occurred on the device network at my place of work, and since I'm the official technician, I'm in charge of dealing with it. Although my major was in networking, I have a very limited practical experience so this may well be a very stupid/easy problem to fix.

Wow great admittance! I respect people that know they are too deep, a trait that is unfortunately getting more rare in the industry.

What are you guys using for security (anti virus, web filter, etc.)? That could be a web filter though usually there's a logo.

Are you guys using any kind of proxy?

Are you using a business-grade router/firewall for your gateway? Is it being properly maintained and support contracts renewed?

Have you changed ISP's or have they introduced DNS filtering security-related services (similar to OpenDNS)?

I think this is what it is as well, alternatively if those machines have any end point security those as well can interrupt requests.

The first things I would do, with network aside do any of these machine have any software in common? AV products? same DNS servers? what are the DNS servers? Google? Router? some other IP?