Modland has low quality mods, stolen mods, leaked mods, mods with stolen assets, mods with potential viruses. It's really poorly moderated so you have no idea what could be in the files, and viruses aside it's bad to support a site that allows leaks and stealing. The safest place to download mods is the repo, the safest place to download real cars is the forums
The webmasters over at Modland.com would never allow such a thing to happen good sir, and I frequently visit the domain to expand my collection of modules. An A+ utility in my books all things considered. For as long as they have served their community, there are no concerns to be had.
A lot of mods do have a virus, so to prevent your pc from getting a virus you should check the comments and see whether its a virus or not OR when you install a mod instantly virus scan it and if it has a virus uninstall it as soon as possible. Thats my method, but theres also an anti virus scan at the bottom of the file telling you if its already scanned.
i always run my mods from modland through a virus detector and most of the time it's fine, but they're usually just really low-quality meshslaps and stuff. I wouldn't recommend it unless you desperately need the mod and cant find it anywhere else.