What made you keep all your coins in the same wallet is the first question that strikes my mind badly.
I don't think that's much of a problem if you for example use a hardware wallet where you physically have to confirm or reject value movements. In that regard, my question would be why OP didn't use a hardware wallet.
People quite often look at the initial purchasing cost and think they can avoid dealing with that by simply using a desktop/mobile client, but that's never a good idea as we can see from the many examples of how people lost their coins. The $100ish they try to save by not purchasing a hardware wallet leads to a loss of thousands of dollars worth of crypto. Pretty sad.
All in all, this looks to me as a lesson learnt. I don't know how many times users such as OP will be suffering from such issues as there's always a new type of scam taking place every single day trying to drag away your money out of your hands. Some people also don't have money to buy that much maybe because they could be from a third world country and/or not too much interested in crypto or have very less (not even $50 worth of BTC or alts) held in their bags for which they don't prefer to go for any hardware wallets.
..... As a result of that, many crypto users do not realize how challenging it is to be their own bank.
That's true, the sort of security we need to take care of is very high in front of what people believe it is. This platform is new and so, chances of getting hacked and scammed are reaching newer peaks every single day with more and more adoption as it's all about getting exposure of these unknown buddies (those who don't know about anything technical) to these highly professional hackers who know how to get into somebody's wallet and get the coins. When we say we are our own bank by using crypto, we really do understand the level risks it possesses and when we put a step in, it's better to be cautious than hell in order to save our everything that's kept in our PC.
Best thing you can do now is to format disk, your OS is completely compromised.
Don't forget to ask him not to save his old Windows.dat (old data) of the previous OS.
@OP, What I didn't get is - when you clicked that suspicious link, wasn't there any Antivirus in your PC that may have stopped or warned you for not visiting there?