For the past several days, Spotify appears to have streamed more than just music to users of its free music service option.

Several users posting on the digital music service’s community forum this week complained about getting hit with malware that caused the default browsers on their systems to automatically open to sites running malicious software. The problem appeared to affect browsers running on Windows and Mac systems.

A Spotify Community forum member first complained about the problem on Tuesday. “If you have Spotify Free open, it will launch - and keep on launching - the default Internet browser on the computer to different kinds of malware / virus sites. Some of them do not even require user action to be able to cause harm,” the user had noted.

After testing the issue on three different computers, the user said the problem most likely had to do with a malicious advertisement, or malvertisement, being served up in Spotify Free.

In an unsigned and unattributed response to the comment, Spotify said it had identified a “small number of users “experiencing problems with questionable website popups via their default browsers. Spotify attributed the problem to an “isolated issue” with an advertisement in its Free tier and claimed it had shut the ad down.

However, a scan of the comments on Spotify Community Friday afternoon showed that some users are continuing to experience problems seemingly related to the issue late this week.

“I am aware of your recent status that the malware ads on Spotify Free has been fixed,” one commenter using the handle sriku91 said Thursday. “However, I still face the problem of such annoying ads opening in any browser I have. This is seriously worrying me not only because of Spotify but the fact that my whole computer is at risk.” The user later reported the problem appeared to have been fixed.

Over the last one day a handful of other users reported failed login attempts to their Google accounts, malware and LAN settings getting automatically changed as the result of a malicious ad being served via Spotify Free.

Malvertisements are online ads with malicious code embedded in them that are often distributed via legitimate online ad platforms and services. Threat actors have increasingly begun using malvertisements because they offer an easier way than other methods for installing malware like data-stealing Trojans, ransomware, and spyware on user systems. In many cases, users only have to visit a website hosting a malicious ad to get infected.

“Apps that appear to be free, which are ad-supported, bring extra risk in the form of malvertising,” says Lysa Myers, security researcher at ESET. “People need to be aware of this extra risk, if they choose to install apps that display ads,” she said.

Users can limit their exposure to malicious ads by being more diligent about the applications they download on their systems. For instance, they can verify if an application or service has been previously associated with malicious ads. “But keep in mind that sometimes these things slip into otherwise high-quality ad networks, so it’s a good idea to keep your software—especially OS, browsers and plug-ins—regularly updated, she says.

It is also important for users to stop assuming the only users on Windows platforms are susceptible to such issues.  “Linux and OS X are not immune, and need to be protected with security software too,” Myers said.

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