While Macs offer strong security protections, they are far from immune to malware, according to new data from security firm Avast.

Since January 2017, Avast has blocked more than 250 million malware threats aimed at their Mac customers.

“Macs are not impervious to malware,” wrote Lukáš Hasik, senior product manager at Avast. “As secure as Macs generally are, the fact is that hackers are targeting them more than ever.”

As Apple’s market share has increased, malware that targets its products has skyrocketed, as TechRepublic’s Jesus Vigo reported. A recent report from Malwarebytes found that Mac malware in 2017 is the highest it has ever been than any other year. And many Macs may be vulnerable to firmware vulnerabilities as well, according to a report from Duo Security.

SEE: Information security incident reporting policy (Tech Pro Research)

Here are the five most common malware threats aimed at Mac users:

1. Adware

Adware represented 17% of the Mac threats found, with 41 million detections. These programs can impact a Mac user’s system in many ways by including sneaking suspicious files into the network, redirecting web searches, and flooding the machine with ads.

2. Blacklisted websites

These malicious sites, representing 14% of threats detected, can wreak havoc as soon as their pages fully load in a browser. They may exploit browser vulnerabilities to send spyware and other unwanted software to the user.

3. Potentially unwanted programs (PUPs)

PUPs are suspicious files that enter a system by attaching themselves to downloads of other programs. They sometimes act as spyware. This type of attack accounted for 5% of malware detections.

4. Trojans

Disguised as legitimate software, Trojans are often used by cybercriminals to gain access to users’ systems and steal data, or gain backdoor access to the system.

5. Ransomware

Rounding out the top five is ransomware, one of the largest threats of the year across all systems. These attacks often enter a computer via a phishing email, and lock files or critical systems until a user agrees to pay a ransom–or has a backup available. However, this is less of a concern for Mac users, as about 99% of ransomware attacks target Microsoft products, according to a recent report from security firm Carbon Black.

It’s likely that Mac malware will continue to grow in 2018, according to the Malwarebytes report.

For tips on how Mac users can best secure their data, click here.