Good.
All the others said is correct: there's much bigger chance that your private key was "leaked" than something on their side. However, the first thing to do is to check your address(es) with another block explorer to make sure indeed your funds are gone and there's no other issue.

About the "leak", there are a lot of ways to happen: from malware and key loggers to accessing a phishing site or storing the data in e-mail, cloud services, or somebody you know physically accessing (your computer/account, or the paper where it was written onto). As you can see, all are on your side (and against you) OP.

But as started: good. Don't use online services to hold your money, especially if you don't believe in their safety (and blockchain.com is old, big and targeted by a lot of phishing). Use something safer. If you don't plan to spend, generate safely(!) a paper wallet and put your (next) bitcoins there. Or use a hardware wallet. Or use air-gaped cold storage, already an USB stick with Tails can do that if you make sure it'll never go online and read how to properly use cold storage.