Xander answered the main question, so I'll focus on the unspoken half of your question - namely, the helpful people at networksecure247.com!
Glancing at their website, I can see:
- Typos in their banners ("Hear to help you")
- Weird formatting for their North America toll-free number (1800 is virtually always shown as '1 800' or '1-800')
- Their telephone support line is a Skype line
- Their website gives me no indication of what they actually do
- Their website doesn't indicate what company they are or where they are registered
- Frequent examples of English usage by a writer that is probably not a native English speaker, and perhaps not even human ("Detect virus and protect PC Less crashes No missing files Stability of computer Less errors Replacing Old PC with new one Buying up a new computer is never a recommended solution to the problem.")
- Their Facebook link doesn't go anywhere
Any of those items alone is something that would embarrass a company and their web designer.
All of these together tell you this website is a scam. The company doesn't exist. It's a front for scam behaviour, so that they might fool their victims who might think I'm not sure exactly what they said, but their website sounds like they know what they're doing...
As Xander explained in a fantastic answer, this company can't know anything about your home computer's security or network settings. They are just phishing, hoping to manipulate you into doing something on your computer to give them access.
These calls can be difficult to interpret for non-technical people. It's always safe to just hang up on anyone calling you. If it was a legitimate, important call, they will follow up, often by mail. It is always best to assume that if you aren't expecting a call, the person is calling you for a reason that benefits them and not you. That applies to "honest" telemarketers as well as scammers.