Lately, there has been a dramatic increase in Phishers everywhere.
If you are randomly added by someone, or in any case, someone asks you to click on a link, be extremely cautious, and look for any spelling mistakes.

A community link is the most common trick
A normal link will look like;
steamcommunity.com
With some extra items to dignify where the link should lead
A common spelling change is;
steamcornmunity.com
cornmunity.com
Corn Munity

If you click on any of these links, I HIGHLY suggest and encourage you to change ALL of your credentials related to anything signed in at the time - Email, Facebook, Steam, etc.

If you accidentally download something from one of these links, you should immediately do a full-scan of your computer for viruses.

In the event of catching a Phisher, report them via the player's Profile for suspected Hijacking/Phishing

If you have or do fall for one of these links, then I can only recommend contacting a Steam employee directly and giving them as much valid information and proof that the account belonged to you, and that certain items where taken from you.

I have personally dealt with 5-7 Automatic Bots, but there are real humans who are phishing as you read this. All you can do is comment on the profile that it's a Phisher, and report them directly.

Thank you, and be safe.