How to find and remove unwanted s/w?

Question

I downloaded free version of ;'Little Snitch'.  It now regularly throws up an invite window to (buy &) upgrade.  This message s/w is what I would dearly love to remove.

Answer 1

Malicious software doesn't always require a administrative password to gain "root" powers, thus control the entire machine, in order to be destructive. It can do a lot just running in what's nicknamed "user space".
Any user level from Guest to Admin can run a program on the machine, as long as this condition exists, the potential for malware being run on the machine exists in some privilege level or another depending upon the users access level.
The intention of some malware may to be to run in a lower privilege mode of the user and monitor the user and or their files for valuable information like credit card numbers and passwords entered, then to pass this information online.
Or it might be that the initial malware could only install a small portion of itself on the users machine, thus needs to "phone home" to download the bigger payload.
There are 65535 networking ports on modern computers, only a small fraction of those ports are used, so it leaves plenty of ports available for other uses, like for malicious purposes.
Compromised web browsers can open new ports to make stealthy connections to command and control servers or to download more malicious software, or even upload the contents of a users files much like users upload files to websites.
Where LittleSnitch comes into play is it's a outgoing firewall, which is the opposite of the incoming firewall in OS X. It watches all processes on the machine and when they attempt to make a outgoing connection it doesn't recognize or it's out of bounds of what it has been allowed, it will then flag the user for approval.
It also has a popup/fade-away window that informs the use of approved software making outgoing/incoming transmissions so in case a approved one (on a approved port) gets compromised (like a browser for instance) it will show unusual activity the user is not requesting.
LittleSnitch keeps the advanced user "in the loop" of the hidden outgoings  with their machine. Apple doesn't employ a outgoing firewall because they don't want to scare users unnecessarily.
LittleSnitch is not a 100% guaranty to prevent malware, it runs in the root level space so it's safe from "user space" malware.
All bets are off if the user gives malware their admin password, thus gaining "root" access, wether or not LS is installed or not.
In the past not many Mac users ran LittleSnitch, however today it's more common and malware writers had to adapt to attempt to remove LS if they gained root access on the machine.
There exists the possibility the malware writer doesn't know about LS, or is careless or can't remove it for some reason or another, which will give the experienced Mac user running LS a upper hand, which they can then notify others of the malware. or unsual outgoing network connections.
Again it's to have more eyes out there watching instead of being blindfolded.