Using the dark web is illegal

This does depend on the country, but in most western countries such as the US, simply visiting the dark web is not illegal. What is illegal is using the dark web for illegal activities like selling drugs (like it is on the clear web or in person).

There are also legitimate and ethical reasons to use the dark web, perhaps the most obvious is bypassing surveillance and censorship in other countries, the anonymity is necessary for journalists and whistleblowers, but with great power comes great responsibility and bad actors who neglect that.

Incognito mode keeps you anonymous

Incognito mode is a tool built-into modern browsers where you can browse the web without the browser saving your search history. While incognito mode is useful, it is not anonymous against your ISP or school network.

Formatting a drive completely removes the data

Formatting a drive deletes the index of the files on it, so it will seem as though the data is gone and your OS will report that the drive is empty. However, the data is still on the hard drive until it is overwritten by new data, and a lot of the time, the data can be recovered.

If you want to securely erase a hard drive, you can use tools like DBAN. Unlike a format, this will take a few hours (depending on the size of the drive and the erasure method), but the data will actually be gone. Alternatively, you can physically destroy the drive if you do not intend to use it again.

Anything harmful is a virus

The general term for software that harms your computer is malware, and a virus is a specific type of malware that modifies and clones itself (much like real life viruses like that make people sick).

Other types of malware include worms, trojans, rogues, spyware, and ransomware. Plus not all threats are the result of malware (e.g., a cybercriminal might hack your computer through vulnerabilities in the OS or your OPSEC). Some hazards are even non-intentional - data loss can occur as a result of hardware failure, human error, fire, flooding etc.

Macs don’t get viruses!

This saying was a lot more common in the 2000s, especially during the period of Apple’s “I’m a Mac and I’m a PC” advertisements. A lot of people have bought a Mac because of this claim because fear sells.

There is some truth to this (viruses are very rare on macOS), but it is horrendously misleading. Notice how people say “Macs don’t get viruses” rather than “Macs don’t get malware”. This wording leaves room for plausible deniability, but people colloquially call any form of malware a virus, so people get the impression that Macs don’t get infected with malware.

In reality, no OS is truly immune from malware and most forms of malware (regardless of the OS) aren’t technically viruses.