If your computer’s connection to the Internet seems to have slowed down lately, it’s possible that it has malware that uses your bandwidth without your knowledge. Finding out about any unauthorized Internet use should be easy enough with a third-party firewall. It should show you a list of all the applications on your computer that try to get on the Internet. Many well-designed malware applications have exceptions added that make it hard for firewalls to report them, though.
There is another way to check
If your firewall won’t tell you much about clandestine attempts by malware on your computer to access the Internet, you could check by hand. If your computer runs XP or a later version of Windows, the Windows netstat command in command prompt is what you need.
To use the netstat command, you need to open command prompt in Administrator mode. In versions of Windows earlier than Windows 8, you simply need to look up a shortcut to command prompt, right-click on it, and then click on Run as administrator . In Windows 8, you have an additional method — you right-click at the bottom left corner of your screen and pick Command prompt (Admin) menu that pops up.
Once command prompt opens (you may see a User Account Control dialog box pop up), you need to type the following string into it: netstat -abf 5 > activity.txt . When you hit Enter , Windows will quietly begin recording every attempt made on your computer to connect to the Internet (you won’t see anything at this stage).
After waiting a minute or two for netstat to record connection attempts, you need to click on the command prompt window to bring focus to it, and then press Ctrl-C . This action copies the Internet connection records created by netstat , pastes them in a text file called activity.txt, and saves it. To view the records on this file, all you need to do is to type the name of the file ( activity.txt) into the command prompt window and hit Enter . Right away, you should see a Notepad file with a long Internet access activity list recorded.
Look for suspicious activity
When you study the list, you should look for the names of processes and websites accessed, that seem unfamiliar. If something seems suspicious, you simply need to search on the Internet for it, to see what it is.
More user-friendly ways exist
If you’d like a less laborious way to spy on your computer’s Internet use, there’s a Windows Sysinternals utility called TCPView that can help you. . You can download it from Microsoft (at technet.microsoft.com/en-us/sysinternals/bb897437.aspx ).
A free, third-party utility called CurrPorts is an excellent, user-friendly way to keep tabs on all the Internet activity on your computer, too