I'd treat free online courses with the same suspicion and aversion I give to free altcoin airdrops.  If it is free, you have to ask yourself what the business model is.  How much personal information do you have to hand over?  Is it something that could lead to identity theft?  Does it involve downloading potentially malicious software?  What's the catch?  Always be mindful of someone trying to exploit you.

You don't even need a course to learn this stuff.  Just stick around these boards for a couple of years and you'll learn plenty.